/* -------------------------------------------------------------
   DESIGN SYSTEM & VARIABLES
   ------------------------------------------------------------- */
:root {
    /* Color Palette - Curated Modern HSL Dark Theme */
    --bg-base: hsl(220, 24%, 7%);
    --bg-surface: hsl(222, 20%, 11%);
    --bg-card: hsla(222, 20%, 15%, 0.6);
    --border-color: hsla(217, 19%, 27%, 0.4);
    --border-hover: hsla(217, 19%, 40%, 0.6);
    
    /* Text Colors */
    --text-primary: hsl(210, 40%, 96%);
    --text-secondary: hsl(215, 20%, 65%);
    --text-muted: hsl(215, 16%, 47%);
    
    /* Accent Colors & Glows */
    --accent-violet: hsl(263, 90%, 62%);
    --accent-violet-glow: hsla(263, 90%, 62%, 0.35);
    
    --accent-cyan: hsl(186, 94%, 43%);
    --accent-cyan-glow: hsla(186, 94%, 43%, 0.3);
    
    /* State Colors */
    --state-success: hsl(142, 70%, 45%);
    --state-success-glow: hsla(142, 70%, 45%, 0.25);
    --state-warning: hsl(38, 92%, 50%);
    --state-warning-glow: hsla(38, 92%, 50%, 0.2);
    --state-danger: hsl(350, 89%, 60%);
    --state-danger-glow: hsla(350, 89%, 60%, 0.2);
    
    /* Layout & Spacing */
    --sidebar-width: 320px;
    --header-height: 70px;
    --radius-sm: 6px;
    --radius-md: 12px;
    --radius-lg: 18px;
    
    /* Fonts */
    --font-sans: 'Inter', system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    --font-mono: 'Fira Code', source-code-pro, Menlo, Monaco, Consolas, "Courier New", monospace;
    
    /* Transition speed */
    --transition-fast: 0.15s ease;
    --transition-normal: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

/* Reset and Base Styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    background-color: var(--bg-base);
    color: var(--text-primary);
    font-family: var(--font-sans);
    height: 100vh;
    overflow: hidden;
    line-height: 1.6;
}

/* Custom Scrollbars */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}
::-webkit-scrollbar-track {
    background: transparent;
}
::-webkit-scrollbar-thumb {
    background: hsl(217, 19%, 20%);
    border-radius: var(--radius-sm);
}
::-webkit-scrollbar-thumb:hover {
    background: hsl(217, 19%, 30%);
}

/* -------------------------------------------------------------
   APP CONTAINERS & LAYOUT
   ------------------------------------------------------------- */
.app-container {
    display: flex;
    flex-direction: column;
    height: 100vh;
}

/* HEADER */
.app-header {
    height: var(--header-height);
    background-color: var(--bg-surface);
    border-bottom: 1px solid var(--border-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 2rem;
    position: relative;
    z-index: 10;
}

.header-logo {
    display: flex;
    align-items: center;
    gap: 0.8rem;
}

.python-logo {
    font-size: 2.2rem;
    background: linear-gradient(135deg, var(--accent-cyan), var(--accent-violet));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    filter: drop-shadow(0 0 8px var(--accent-violet-glow));
}

.logo-text h1 {
    font-size: 1.25rem;
    font-weight: 800;
    letter-spacing: -0.5px;
    color: var(--text-primary);
}

.logo-text span {
    font-size: 0.75rem;
    color: var(--text-muted);
    font-weight: 500;
}

.header-status {
    display: flex;
    align-items: center;
}

.status-badge {
    display: flex;
    align-items: center;
    gap: 0.6rem;
    padding: 0.5rem 1rem;
    border-radius: 50px;
    font-size: 0.8rem;
    font-weight: 600;
    border: 1px solid transparent;
}

.status-badge.loading {
    background-color: var(--state-warning-glow);
    color: var(--state-warning);
    border-color: hsla(38, 92%, 50%, 0.3);
}

.status-badge.ready {
    background-color: var(--state-success-glow);
    color: var(--state-success);
    border-color: hsla(142, 70%, 45%, 0.3);
    box-shadow: 0 0 10px var(--state-success-glow);
}

/* MAIN LAYOUT */
.main-layout {
    display: flex;
    flex: 1;
    height: calc(100vh - var(--header-height));
    overflow: hidden;
}

/* -------------------------------------------------------------
   SIDEBAR & NAVIGATION
   ------------------------------------------------------------- */
.sidebar {
    width: var(--sidebar-width);
    background-color: var(--bg-surface);
    border-right: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    overflow-y: auto;
}

.progress-section {
    padding: 1.5rem;
    border-bottom: 1px solid var(--border-color);
}

.progress-info {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 0.5rem;
}

.progress-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    font-weight: 600;
}

.progress-value {
    font-size: 0.95rem;
    color: var(--accent-cyan);
    font-weight: 700;
}

.progress-track {
    height: 8px;
    background-color: hsl(217, 19%, 20%);
    border-radius: 50px;
    overflow: hidden;
    margin-bottom: 0.4rem;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--accent-cyan), var(--accent-violet));
    border-radius: 50px;
    transition: width var(--transition-normal);
    box-shadow: 0 0 8px var(--accent-cyan-glow);
}

.progress-stats {
    font-size: 0.75rem;
    color: var(--text-muted);
}

/* Curriculum Menu Tree */
.curriculum-nav {
    flex: 1;
    overflow-y: auto;
    padding: 1rem 0;
}

.nav-loading {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 0.5rem;
    color: var(--text-muted);
    font-size: 0.9rem;
    padding: 2rem;
}

/* Module Header Item */
.module-group {
    margin-bottom: 0.5rem;
}

.module-header {
    width: 100%;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.8rem 1.2rem;
    background: transparent;
    border: none;
    color: var(--text-primary);
    font-weight: 700;
    font-size: 0.85rem;
    cursor: pointer;
    text-align: left;
    transition: background-color var(--transition-fast);
}

.module-header:hover {
    background-color: hsl(217, 19%, 15%);
}

.module-title-box {
    display: flex;
    flex-direction: column;
    gap: 0.1rem;
}

.module-meta {
    font-size: 0.7rem;
    color: var(--accent-violet);
    font-weight: 600;
    text-transform: uppercase;
}

.module-header i.fa-chevron-down {
    font-size: 0.75rem;
    color: var(--text-muted);
    transition: transform var(--transition-normal);
}

.module-group.expanded .module-header i.fa-chevron-down {
    transform: rotate(180deg);
}

.lesson-list {
    display: none;
    list-style: none;
    padding: 0 0.5rem;
    margin-top: 0.2rem;
}

.module-group.expanded .lesson-list {
    display: block;
}

/* Lesson Navigation Item */
.lesson-item {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0.6rem 1rem;
    margin: 0.2rem 0;
    border-radius: var(--radius-sm);
    color: var(--text-secondary);
    font-size: 0.8rem;
    font-weight: 500;
    cursor: pointer;
    transition: all var(--transition-fast);
    user-select: none;
}

.lesson-item:hover {
    background-color: hsl(217, 19%, 18%);
    color: var(--text-primary);
}

.lesson-item.active {
    background-color: var(--accent-violet-glow);
    color: var(--text-primary);
    border-left: 3px solid var(--accent-violet);
}

.lesson-title-text {
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    margin-right: 0.5rem;
    flex: 1;
}

.lesson-status-icon {
    font-size: 0.85rem;
}

.lesson-status-icon.completed {
    color: var(--state-success);
}

.lesson-status-icon.unlocked {
    color: var(--text-muted);
}

.lesson-status-icon.locked {
    color: var(--text-muted);
    opacity: 0.4;
}

.lesson-item.locked-state {
    opacity: 0.5;
    cursor: not-allowed;
}

.lesson-item.locked-state:hover {
    background-color: transparent;
    color: var(--text-secondary);
}

.sidebar-footer {
    padding: 1rem 1.5rem;
    border-top: 1px solid var(--border-color);
}

/* -------------------------------------------------------------
   WORKSPACE & PANES
   ------------------------------------------------------------- */
.workspace {
    display: flex;
    flex: 1;
    overflow: hidden;
}

.workspace-pane {
    flex: 1;
    height: 100%;
    overflow-y: auto;
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
}

.lesson-pane {
    border-right: 1px solid var(--border-color);
    max-width: 55%;
}

.playground-pane {
    background-color: hsl(220, 24%, 6%);
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

/* -------------------------------------------------------------
   LESSON INTERFACE (Left Pane)
   ------------------------------------------------------------- */
.lesson-card {
    display: flex;
    flex-direction: column;
    height: 100%;
}

.lesson-nav-header {
    display: flex;
    gap: 0.6rem;
    margin-bottom: 0.5rem;
}

.module-tag {
    font-size: 0.7rem;
    font-weight: 700;
    text-transform: uppercase;
    background-color: hsl(217, 19%, 18%);
    color: var(--text-secondary);
    padding: 0.2rem 0.5rem;
    border-radius: 4px;
}

.lesson-tag {
    font-size: 0.7rem;
    font-weight: 700;
    text-transform: uppercase;
    background-color: var(--accent-violet-glow);
    color: var(--text-primary);
    padding: 0.2rem 0.5rem;
    border-radius: 4px;
}

.lesson-title {
    font-size: 1.6rem;
    font-weight: 800;
    margin-bottom: 1.2rem;
    letter-spacing: -0.5px;
    background: linear-gradient(to right, var(--text-primary), hsl(210, 40%, 80%));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

/* Tabs */
.tab-container {
    display: flex;
    border-bottom: 1px solid var(--border-color);
    margin-bottom: 1.2rem;
}

.tab-btn {
    background: none;
    border: none;
    color: var(--text-secondary);
    padding: 0.75rem 1.25rem;
    font-size: 0.85rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-fast);
    position: relative;
    display: flex;
    align-items: center;
    gap: 0.4rem;
}

.tab-btn:hover {
    color: var(--text-primary);
}

.tab-btn.active {
    color: var(--accent-cyan);
}

.tab-btn.active::after {
    content: '';
    position: absolute;
    bottom: -1px;
    left: 0;
    right: 0;
    height: 2px;
    background-color: var(--accent-cyan);
    box-shadow: 0 0 8px var(--accent-cyan-glow);
}

.badge.dot {
    width: 6px;
    height: 6px;
    background-color: var(--state-warning);
    border-radius: 50%;
    display: inline-block;
}

/* Tab Contents */
.tab-content {
    display: none;
    flex: 1;
    overflow-y: auto;
    padding-bottom: 1.5rem;
}

.tab-content.active {
    display: flex;
    flex-direction: column;
}

/* Explanation / Markdown styling */
.lesson-content-body {
    font-size: 0.95rem;
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
}

.lesson-content-body p {
    margin-bottom: 1rem;
}

.lesson-content-body code {
    background-color: hsl(217, 19%, 15%);
    color: var(--accent-cyan);
    padding: 0.15rem 0.35rem;
    border-radius: 4px;
    font-family: var(--font-mono);
    font-size: 0.85rem;
}

.lesson-content-body ul, .lesson-content-body ol {
    margin-left: 1.5rem;
    margin-bottom: 1rem;
}

.lesson-content-body li {
    margin-bottom: 0.4rem;
}

.lesson-content-body h3, .lesson-content-body h4 {
    color: var(--text-primary);
    margin: 1.5rem 0 0.8rem;
    font-weight: 700;
}

.lesson-content-body h3 {
    font-size: 1.15rem;
}

/* Callouts */
.callout {
    background-color: var(--accent-violet-glow);
    border-left: 4px solid var(--accent-violet);
    padding: 1rem;
    border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
    margin: 1.2rem 0;
    font-size: 0.9rem;
    color: var(--text-primary);
}

.callout.tip {
    background-color: var(--state-success-glow);
    border-left-color: var(--state-success);
}

.callout-title {
    font-weight: 700;
    margin-bottom: 0.3rem;
    display: flex;
    align-items: center;
    gap: 0.4rem;
}

/* Sample Code block */
.sample-code-container {
    background-color: hsl(220, 24%, 5%);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 1.2rem;
    position: relative;
    margin-bottom: 1.5rem;
}

.sample-code-container h3 {
    font-size: 0.8rem;
    text-transform: uppercase;
    color: var(--text-muted);
    letter-spacing: 0.5px;
    margin-bottom: 0.8rem;
    display: flex;
    align-items: center;
    gap: 0.4rem;
}

.sample-code-container pre {
    margin: 0;
    overflow-x: auto;
}

.sample-code-container code {
    font-family: var(--font-mono);
    font-size: 0.85rem;
    color: hsl(210, 40%, 90%);
}

.btn-copy {
    position: absolute;
    top: 1rem;
    right: 1rem;
    background: hsl(217, 19%, 15%);
    border: 1px solid var(--border-color);
    color: var(--text-secondary);
    padding: 0.4rem 0.8rem;
    border-radius: 6px;
    font-size: 0.75rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-fast);
    display: flex;
    align-items: center;
    gap: 0.3rem;
}

.btn-copy:hover {
    background: hsl(217, 19%, 20%);
    color: var(--text-primary);
    border-color: var(--border-hover);
}

/* QUIZ STYLES */
.quiz-container {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.quiz-question-card {
    background-color: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 1.2rem;
    transition: border-color var(--transition-fast);
}

.quiz-question-card:hover {
    border-color: var(--border-hover);
}

.quiz-q-num {
    font-size: 0.75rem;
    color: var(--accent-cyan);
    font-weight: 700;
    text-transform: uppercase;
    margin-bottom: 0.4rem;
}

.quiz-q-text {
    font-size: 0.95rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 1rem;
}

.quiz-options {
    display: flex;
    flex-direction: column;
    gap: 0.6rem;
}

.quiz-option {
    display: flex;
    align-items: center;
    gap: 0.8rem;
    padding: 0.75rem 1rem;
    background-color: hsl(217, 19%, 13%);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 0.85rem;
    color: var(--text-secondary);
    transition: all var(--transition-fast);
}

.quiz-option:hover {
    background-color: hsl(217, 19%, 17%);
    color: var(--text-primary);
    border-color: var(--border-hover);
}

.quiz-option.selected {
    background-color: var(--accent-violet-glow);
    border-color: var(--accent-violet);
    color: var(--text-primary);
}

.quiz-option.correct {
    background-color: var(--state-success-glow);
    border-color: var(--state-success);
    color: var(--text-primary);
}

.quiz-option.incorrect {
    background-color: var(--state-danger-glow);
    border-color: var(--state-danger);
    color: var(--text-primary);
}

.quiz-radio {
    width: 16px;
    height: 16px;
    border: 2px solid var(--text-muted);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
    transition: all var(--transition-fast);
}

.quiz-option.selected .quiz-radio {
    border-color: var(--accent-violet);
    background-color: var(--accent-violet);
}

.quiz-option.selected .quiz-radio::after {
    content: '';
    width: 6px;
    height: 6px;
    background-color: var(--text-primary);
    border-radius: 50%;
}

.quiz-option.correct .quiz-radio {
    border-color: var(--state-success);
    background-color: var(--state-success);
}

.quiz-option.incorrect .quiz-radio {
    border-color: var(--state-danger);
    background-color: var(--state-danger);
}

/* CHALLENGE STYLES */
.exercise-instruction-box {
    background-color: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 1.2rem;
    margin-bottom: 1rem;
}

.exercise-instruction-box h3 {
    font-size: 0.85rem;
    color: var(--accent-cyan);
    text-transform: uppercase;
    margin-bottom: 0.6rem;
    display: flex;
    align-items: center;
    gap: 0.4rem;
}

#exercise-instructions {
    font-size: 0.95rem;
    color: var(--text-secondary);
}

#exercise-instructions p {
    margin-bottom: 0.6rem;
}

#exercise-instructions code {
    background-color: hsl(217, 19%, 15%);
    color: var(--accent-cyan);
    padding: 0.1rem 0.3rem;
    border-radius: 4px;
    font-family: var(--font-mono);
}

/* Hints Accordion */
.hints-accordion {
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    background-color: hsl(217, 19%, 11%);
    overflow: hidden;
}

.accordion-header {
    padding: 1rem 1.2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    cursor: pointer;
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-secondary);
    user-select: none;
    transition: all var(--transition-fast);
}

.accordion-header:hover {
    color: var(--text-primary);
    background-color: hsl(217, 19%, 14%);
}

.accordion-header i.fa-chevron-down {
    transition: transform var(--transition-normal);
}

.hints-accordion.open .accordion-header i.fa-chevron-down {
    transform: rotate(180deg);
}

.accordion-content {
    display: none;
    padding: 1rem 1.2rem;
    border-top: 1px solid var(--border-color);
    font-size: 0.85rem;
    color: var(--text-muted);
    background-color: hsl(220, 24%, 8%);
}

.hints-accordion.open .accordion-content {
    display: block;
}

/* Feedback box */
.feedback-box {
    padding: 1rem;
    border-radius: var(--radius-sm);
    font-size: 0.85rem;
    font-weight: 500;
    margin-top: 1rem;
}

.feedback-box.success {
    background-color: var(--state-success-glow);
    border: 1px solid hsla(142, 70%, 45%, 0.3);
    color: hsl(142, 70%, 75%);
}

.feedback-box.error {
    background-color: var(--state-danger-glow);
    border: 1px solid hsla(350, 89%, 60%, 0.3);
    color: hsl(350, 89%, 75%);
}

/* Bottom Navigation Controls */
.lesson-navigation {
    display: flex;
    justify-content: space-between;
    margin-top: auto;
    padding-top: 2rem;
    border-top: 1px solid var(--border-color);
    gap: 1rem;
}

/* -------------------------------------------------------------
   PLAYGROUND WORKSPACE (Right Pane)
   ------------------------------------------------------------- */
.card {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    overflow: hidden;
    display: flex;
    flex-direction: column;
}

/* Window Chrome styling */
.window-header {
    height: 40px;
    background-color: hsl(222, 20%, 9%);
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    padding: 0 1.2rem;
    justify-content: space-between;
    user-select: none;
}

.window-controls {
    display: flex;
    gap: 6px;
    align-items: center;
}

.window-controls .dot {
    width: 10px;
    height: 10px;
    border-radius: 50%;
    display: inline-block;
}

.window-controls .dot.red { background-color: hsl(350, 80%, 60%); }
.window-controls .dot.yellow { background-color: hsl(38, 85%, 60%); }
.window-controls .dot.green { background-color: hsl(142, 70%, 50%); }

.window-title {
    font-size: 0.75rem;
    color: var(--text-secondary);
    font-family: var(--font-mono);
    font-weight: 500;
    display: flex;
    align-items: center;
    gap: 0.4rem;
}

.window-actions {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

/* EDITOR ENGINE */
.editor-window {
    flex: 2;
    min-height: 250px;
}

.editor-body {
    flex: 1;
    display: flex;
    background-color: hsl(220, 24%, 4%);
    overflow: hidden;
}

.editor-container {
    flex: 1;
    display: flex;
    overflow: hidden;
}

.line-numbers {
    padding: 1.2rem 0.8rem;
    text-align: right;
    color: hsl(217, 10%, 38%);
    font-family: var(--font-mono);
    font-size: 0.85rem;
    background-color: hsl(220, 24%, 3%);
    border-right: 1px solid var(--border-color);
    user-select: none;
    line-height: 1.5;
    white-space: pre;
    flex-shrink: 0;
}

/* Shared code area: textarea and highlight layer stacked */
.editor-code-area {
    position: relative;
    flex: 1;
    overflow: auto;
}

/* ── Highlight pre-layer (sits behind textarea) ── */
.editor-highlight {
    position: absolute;
    top: 0;
    left: 0;
    margin: 0;
    padding: 1.2rem;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    line-height: 1.5;
    white-space: pre;
    word-break: normal;
    overflow-wrap: normal;
    tab-size: 4;
    pointer-events: none;
    min-width: 100%;
    min-height: 100%;
    color: hsl(210, 15%, 80%);   /* default code color */
    background: transparent;
    box-sizing: border-box;
    z-index: 1;
}

.editor-highlight code {
    font-family: inherit;
    font-size: inherit;
    background: none;
    color: inherit;
    padding: 0;
}

/* ── Textarea on top, text is transparent (caret still visible) ── */
#code-editor {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    margin: 0;
    padding: 1.2rem;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    line-height: 1.5;
    tab-size: 4;
    background: transparent;
    border: none;
    outline: none;
    resize: none;
    white-space: pre;
    overflow: auto;
    /* Text is invisible — the highlight layer shows through */
    color: transparent;
    caret-color: hsl(210, 40%, 90%);
    z-index: 2;
    box-sizing: border-box;
}

/* ── Syntax Highlight Colour Classes (VS Code Dark+ palette, neutral) ── */
/* Keywords: def, class, if, for, return … */
.hl-keyword  { color: #569CD6; }
/* Built-in functions: print, len, range … */
.hl-builtin  { color: #4EC9B0; }
/* Function name after def */
.hl-funcname { color: #DCDCAA; }
/* Class name after class */
.hl-classname{ color: #4EC9B0; }
/* String literals */
.hl-string   { color: #CE9178; }
/* Comments */
.hl-comment  { color: #6A9955; font-style: italic; }
/* Numbers */
.hl-number   { color: #B5CEA8; }
/* Decorators @… */
.hl-decorator{ color: #C586C0; }
/* Operators / punctuation (subtle) */
.hl-operator { color: #D4D4D4; }


/* ACTION CONTROLS */
.action-bar {
    display: flex;
    gap: 1rem;
}

.action-bar button {
    flex: 1;
}

/* TERMINAL SCREEN */
.terminal-window {
    flex: 1.2;
    min-height: 150px;
}

.terminal-body {
    flex: 1;
    background-color: hsl(220, 24%, 3%);
    padding: 1rem;
    font-family: var(--font-mono);
    font-size: 0.85rem;
    overflow-y: auto;
    display: flex;
    flex-direction: column;
    gap: 0.4rem;
    color: var(--text-secondary);
}

.terminal-line {
    word-break: break-all;
    white-space: pre-wrap;
    line-height: 1.4;
}

.terminal-line.output {
    color: var(--text-primary);
}

.terminal-line.error {
    color: var(--state-danger);
}

.terminal-line.success {
    color: var(--state-success);
}

.terminal-line.system-msg {
    color: var(--accent-cyan);
    opacity: 0.85;
}

.terminal-line.prompt {
    color: var(--accent-violet);
    font-weight: bold;
}

/* RESULTS POPUP PANEL */
.results-panel {
    background-color: var(--bg-surface);
    border: 1px solid var(--border-color);
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.4);
    transition: all var(--transition-normal);
}

.results-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.8rem 1.2rem;
    border-bottom: 1px solid var(--border-color);
}

.results-header h3 {
    font-size: 0.9rem;
    color: var(--text-primary);
}

.btn-close {
    background: none;
    border: none;
    color: var(--text-muted);
    font-size: 1.2rem;
    cursor: pointer;
    transition: color var(--transition-fast);
}

.btn-close:hover {
    color: var(--text-primary);
}

.results-list {
    padding: 1rem;
    display: flex;
    flex-direction: column;
    gap: 0.6rem;
    max-height: 250px;
    overflow-y: auto;
}

.test-item {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0.6rem 0.8rem;
    border-radius: var(--radius-sm);
    font-size: 0.8rem;
}

.test-item.pass {
    background-color: var(--state-success-glow);
    border: 1px solid hsla(142, 70%, 45%, 0.2);
    color: hsl(142, 70%, 80%);
}

.test-item.fail {
    background-color: var(--state-danger-glow);
    border: 1px solid hsla(350, 89%, 60%, 0.2);
    color: hsl(350, 89%, 80%);
}

.test-item-title {
    font-weight: 600;
}

.test-status-badge {
    font-size: 0.75rem;
    font-weight: bold;
    text-transform: uppercase;
}

/* -------------------------------------------------------------
   BUTTON COMPONENTS (Vanilla CSS UX Boost)
   ------------------------------------------------------------- */
button {
    font-family: var(--font-sans);
    cursor: pointer;
}

.btn-primary {
    background: linear-gradient(135deg, var(--accent-violet), hsl(263, 75%, 55%));
    border: none;
    color: var(--text-primary);
    padding: 0.75rem 1.5rem;
    border-radius: var(--radius-md);
    font-weight: 600;
    font-size: 0.9rem;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    box-shadow: 0 4px 12px var(--accent-violet-glow);
    transition: all var(--transition-fast);
}

.btn-primary:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: 0 6px 18px hsla(263, 90%, 62%, 0.5);
}

.btn-primary:active:not(:disabled) {
    transform: translateY(0);
}

.btn-primary:disabled {
    background: hsl(217, 19%, 15%);
    color: var(--text-muted);
    box-shadow: none;
    cursor: not-allowed;
}

.btn-secondary {
    background: hsl(217, 19%, 15%);
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    padding: 0.75rem 1.5rem;
    border-radius: var(--radius-md);
    font-weight: 600;
    font-size: 0.9rem;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    transition: all var(--transition-fast);
}

.btn-secondary:hover:not(:disabled) {
    background: hsl(217, 19%, 20%);
    border-color: var(--border-hover);
}

.btn-secondary:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

.btn-success {
    background: linear-gradient(135deg, var(--state-success), hsl(142, 60%, 40%));
    border: none;
    color: var(--text-primary);
    padding: 0.75rem 1.5rem;
    border-radius: var(--radius-md);
    font-weight: 600;
    font-size: 0.9rem;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    box-shadow: 0 4px 12px var(--state-success-glow);
    transition: all var(--transition-fast);
}

.btn-success:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: 0 6px 18px hsla(142, 70%, 45%, 0.4);
}

.btn-success:active:not(:disabled) {
    transform: translateY(0);
}

.btn-success:disabled {
    background: hsl(217, 19%, 15%);
    color: var(--text-muted);
    box-shadow: none;
    cursor: not-allowed;
}

.btn-full {
    width: 100%;
}

.btn-small {
    padding: 0.4rem 0.8rem;
    font-size: 0.75rem;
    border-radius: var(--radius-sm);
}

.btn-icon {
    background: none;
    border: none;
    color: var(--text-secondary);
    font-size: 0.95rem;
    padding: 0.3rem;
    border-radius: 4px;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all var(--transition-fast);
}

.btn-icon:hover {
    background-color: hsl(217, 19%, 15%);
    color: var(--text-primary);
}

.btn-icon-text {
    background: none;
    border: none;
    color: var(--text-secondary);
    font-size: 0.75rem;
    display: flex;
    align-items: center;
    gap: 0.3rem;
    padding: 0.3rem 0.5rem;
    border-radius: 4px;
    font-weight: 600;
    transition: all var(--transition-fast);
}

.btn-icon-text:hover {
    background-color: hsl(217, 19%, 15%);
    color: var(--text-primary);
}

/* ============================================================ */
/* MOBILE RESPONSIVENESS OVERRIDES */
/* ============================================================ */

/* Mobile Menu Button - Hidden on desktop */
.btn-mobile-menu {
    display: none;
    background: none;
    border: none;
    color: var(--text-primary);
    font-size: 1.5rem;
    cursor: pointer;
    margin-right: 1rem;
    padding: 0.5rem;
}

@media (max-width: 1024px) {
    /* Base Body Constraints to prevent mobile Safari bounce/horizontal scroll */
    body {
        overflow: hidden; /* App-like container */
        position: fixed;
        width: 100%;
        height: 100%;
    }

    .btn-mobile-menu {
        display: block;
    }

    /* Header Wrap */
    .app-header {
        flex-wrap: wrap;
        height: auto;
        padding: 0.75rem 1rem;
        gap: 1rem;
    }
    
    .header-progress {
        order: 3;
        width: 100%;
        max-width: 100%;
    }
    
    .header-status {
        order: 2;
        gap: 0.5rem;
    }

    .btn-header {
        margin-right: 0;
        padding: 0.5rem;
        font-size: 0.8rem;
    }

    /* Main Layout into column */
    .main-layout {
        flex-direction: column;
        position: relative;
    }

    /* Off-Canvas Sidebar */
    .sidebar {
        position: absolute;
        top: 0;
        left: -320px;
        width: 320px;
        max-width: 80vw;
        height: 100%;
        z-index: 100;
        transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
        box-shadow: 5px 0 15px rgba(0,0,0,0.5);
    }
    .sidebar.mobile-open {
        transform: translateX(320px);
    }

    /* Workspace */
    .workspace {
        flex-direction: column;
        height: 100%;
        flex: 1;
        overflow: hidden; /* Let inner panes scroll */
    }

    .workspace-pane {
        width: 100%;
        max-width: 100vw;
    }

    /* Lesson Pane Height Constraint */
    .lesson-pane {
        height: 50%;
        border-right: none;
        border-bottom: 2px solid var(--border-color);
        max-width: 100vw;
    }

    /* Playground Area */
    .playground-pane {
        height: 50%;
        min-height: 250px;
    }
    
    .editor-container {
        height: calc(100% - 150px);
    }

    /* Modals */
    .modal-content, .dsa-modal-content {
        width: 95vw;
        max-width: 95vw;
        margin: 0 auto;
        height: 90vh;
    }
    
    /* Reference Modal Split Pane becomes Vertical Stack */
    .modal-body {
        grid-template-columns: 1fr;
        grid-template-rows: auto 1fr;
        padding: 0;
    }
    .modal-nav {
        border-right: none;
        border-bottom: 1px solid var(--border-color);
        padding: 0.5rem;
        display: flex;
        overflow-x: auto;
        white-space: nowrap;
        scrollbar-width: none; /* Hide scrollbar for clean look */
    }
    .modal-nav::-webkit-scrollbar { display: none; }
    
    .modal-nav ul {
        display: flex;
        gap: 0.5rem;
    }
    .modal-nav li {
        margin-bottom: 0;
    }
    .modal-nav a {
        background: var(--bg-card);
        white-space: nowrap;
    }

    .modal-content-area {
        padding: 1rem;
    }

    /* Touch Targets (Minimum 44px for Apple HIG) */
    .btn-primary, .btn-secondary, .lesson-nav-tab, .btn-header {
        min-height: 44px;
        display: flex;
        align-items: center;
        justify-content: center;
    }
}

/* Very small screens (iPhone SE, etc) */
@media (max-width: 400px) {
    .header-logo span {
        font-size: 1rem;
    }
    .btn-header span {
        display: none; /* Icon only on very small screens */
    }
    .dsa-problems-grid {
        grid-template-columns: 1fr;
    }
}

/* ============================================================ */
/* NEW FEATURES: REFERENCE MODAL & SANDBOX MODE */
/* ============================================================ */

/* Header Buttons */
.btn-header {
    margin-right: 12px;
    padding: 0.5rem 1rem;
    font-size: 0.85rem;
    background: hsla(217, 19%, 20%, 0.5); /* Adjusted from broken variable */
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    border-radius: var(--radius-md);
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    transition: all 0.2s ease;
}
.btn-header:hover {
    background: var(--bg-card);
    border-color: var(--text-secondary);
}

#btn-reference-guide {
    background: linear-gradient(135deg, hsl(263, 60%, 30%), hsl(263, 80%, 20%));
    border: 1px solid var(--accent-violet);
    box-shadow: 0 0 10px var(--accent-violet-glow);
}
#btn-reference-guide:hover {
    background: linear-gradient(135deg, hsl(263, 70%, 40%), hsl(263, 90%, 30%));
    box-shadow: 0 0 15px var(--accent-violet-glow);
    color: white;
}

#btn-sandbox-mode {
    background: linear-gradient(135deg, hsl(186, 70%, 20%), hsl(186, 90%, 15%));
    border: 1px solid var(--accent-cyan);
    box-shadow: 0 0 10px var(--accent-cyan-glow);
}
#btn-sandbox-mode:hover {
    background: linear-gradient(135deg, hsl(186, 80%, 25%), hsl(186, 95%, 20%));
    box-shadow: 0 0 15px var(--accent-cyan-glow);
    color: white;
}

.header-status {
    display: flex;
    align-items: center;
}

/* Sandbox Mode Layout Overrides */
.main-layout.sandbox-active .sidebar,
.main-layout.sandbox-active .lesson-pane {
    display: none !important;
}
.main-layout.sandbox-active .playground-pane {
    flex: 1;
    max-width: 100%;
}
.sandbox-active #btn-submit-solution {
    display: none;
}

/* Modal Overlay */
.modal-overlay {
    position: fixed;
    top: 0; left: 0; width: 100%; height: 100%;
    background: rgba(0, 0, 0, 0.7);
    backdrop-filter: blur(8px);
    z-index: 9999; /* Increased z-index to ensure it sits above everything */
    display: flex;
    align-items: center;
    justify-content: center;
    animation: fadeIn 0.2s ease;
}

/* Modal Content Box */
.modal-content {
    background: var(--bg-surface);
    width: 900px;
    max-width: 95%;
    max-height: 85vh;
    border-radius: var(--radius-lg);
    border: 1px solid var(--border-color);
    box-shadow: 0 20px 40px rgba(0,0,0,0.8);
    display: flex;
    flex-direction: column;
}

/* Modal Header */
.modal-header {
    padding: 1.5rem 2rem;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: var(--bg-card);
    border-radius: var(--radius-lg) var(--radius-lg) 0 0;
}
.modal-header h2 {
    margin: 0;
    font-size: 1.5rem;
    color: var(--text-primary);
    display: flex;
    align-items: center;
    gap: 0.75rem;
}
.modal-header h2 i {
    color: var(--accent-violet);
}
.btn-close-modal {
    background: none;
    border: none;
    color: var(--text-muted);
    font-size: 2.5rem;
    cursor: pointer;
    line-height: 1;
    padding: 0;
    transition: color 0.2s;
}
.btn-close-modal:hover {
    color: var(--state-danger);
}

/* Modal Body */
.modal-body {
    padding: 0;
    overflow-y: auto;
    display: grid;
    grid-template-columns: 250px 1fr;
    height: 100%;
}

.modal-nav {
    background: var(--bg-base);
    border-right: 1px solid var(--border-color);
    padding: 1.5rem 1rem;
    overflow-y: auto;
}

.modal-nav ul {
    list-style: none;
    padding: 0;
    margin: 0;
}

.modal-nav li {
    margin-bottom: 0.5rem;
}

.modal-nav a {
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 0.95rem;
    display: block;
    padding: 0.5rem 1rem;
    border-radius: var(--radius-sm);
    transition: all 0.2s;
}

.modal-nav a:hover {
    background: var(--bg-card);
    color: var(--text-primary);
}

.modal-content-area {
    padding: 2rem;
    overflow-y: auto;
    scroll-behavior: smooth;
}

.modal-content-area h3 {
    color: var(--accent-cyan);
    margin-top: 2.5rem;
    margin-bottom: 1rem;
    font-size: 1.4rem;
    padding-bottom: 0.5rem;
    border-bottom: 1px solid var(--border-color);
}
.modal-content-area h3:first-child {
    margin-top: 0;
}
.modal-content-area pre {
    background: var(--bg-base);
    padding: 1.25rem;
    border-radius: var(--radius-sm);
    border: 1px solid var(--border-color);
    margin-bottom: 1.5rem;
    font-family: var(--font-mono);
    font-size: 0.95rem;
    color: var(--text-primary);
    overflow-x: auto;
}

.modal-content-area pre code {
    color: var(--text-primary);
}

.modal-content-area p {
    color: var(--text-secondary);
    line-height: 1.6;
    margin-bottom: 1rem;
}

.syntax-keyword { color: hsl(300, 70%, 60%); }
.syntax-string { color: hsl(140, 60%, 50%); }
.syntax-comment { color: var(--text-muted); font-style: italic; }
.syntax-func { color: hsl(210, 80%, 60%); }
.syntax-number { color: hsl(30, 80%, 60%); }

@keyframes fadeIn {
    from { opacity: 0; transform: scale(0.98); }
    to { opacity: 1; transform: scale(1); }
}

/* ============================================================ */
/* NEW FEATURE: DSA PRACTICE ARENA */
/* ============================================================ */

#btn-dsa-practice {
    background: linear-gradient(135deg, hsl(32, 90%, 45%), hsl(15, 90%, 40%));
    border: 1px solid hsl(32, 90%, 55%);
    box-shadow: 0 0 10px hsla(32, 90%, 50%, 0.4);
}
#btn-dsa-practice:hover {
    background: linear-gradient(135deg, hsl(32, 95%, 50%), hsl(15, 95%, 45%));
    box-shadow: 0 0 15px hsla(32, 90%, 50%, 0.6);
    color: white;
}

/* DSA Modal Specifics */
.dsa-modal-content {
    width: 1000px;
    max-height: 90vh;
}
.dsa-modal-body {
    display: flex;
    flex-direction: column;
    padding: 2rem;
    overflow-y: hidden;
}
.dsa-intro {
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
    font-size: 1.1rem;
}
.dsa-filters {
    display: flex;
    gap: 1rem;
    margin-bottom: 1.5rem;
}
.btn-filter {
    background: var(--bg-base);
    border: 1px solid var(--border-color);
    color: var(--text-secondary);
    padding: 0.5rem 1rem;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-size: 0.9rem;
    transition: all 0.2s;
}
.btn-filter:hover, .btn-filter.active {
    background: var(--bg-card);
    color: var(--text-primary);
    border-color: var(--accent-cyan);
}

.dsa-problems-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 1rem;
    overflow-y: auto;
    padding-right: 0.5rem;
    padding-bottom: 1rem;
}

.dsa-problem-card {
    background: var(--bg-base);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    padding: 1.25rem;
    cursor: pointer;
    transition: all 0.2s ease;
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}
.dsa-problem-card:hover {
    transform: translateY(-2px);
    border-color: var(--accent-violet);
    box-shadow: 0 5px 15px rgba(0,0,0,0.3);
}

.dsa-card-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
}
.dsa-card-title {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin: 0;
}
.dsa-tag {
    font-size: 0.75rem;
    padding: 0.2rem 0.5rem;
    border-radius: 4px;
    font-weight: 600;
}
.dsa-tag.easy { background: hsla(142, 70%, 45%, 0.2); color: hsl(142, 70%, 60%); }
.dsa-tag.medium { background: hsla(38, 92%, 50%, 0.2); color: hsl(38, 92%, 60%); }
.dsa-tag.hard { background: hsla(350, 89%, 60%, 0.2); color: hsl(350, 89%, 70%); }
.dsa-topic {
    font-size: 0.8rem;
    color: var(--text-muted);
}

/* DSA Mode Layout Overrides */
.main-layout.dsa-mode-active .sidebar,
.main-layout.dsa-mode-active .lesson-pane {
    display: none !important;
}
.main-layout.dsa-mode-active #dsa-description-pane {
    display: flex !important;
}

.dsa-card {
    display: flex;
    flex-direction: column;
    height: 100%;
}
.dsa-description-body {
    flex: 1;
    overflow-y: auto;
    color: var(--text-secondary);
    line-height: 1.6;
    font-size: 1.05rem;
    padding-bottom: 2rem;
}
.dsa-description-body code {
    background: var(--bg-base);
    color: var(--accent-cyan);
    padding: 0.1rem 0.4rem;
    border-radius: 4px;
    font-family: var(--font-mono);
    font-size: 0.9em;
}