:root {
    /* Color Palette - Premium Dark Theme */
    --bg-main: #0b0f19;
    --bg-card: rgba(30, 41, 59, 0.7);
    --bg-hover: rgba(51, 65, 85, 0.8);
    
    --text-main: #f8fafc;
    --text-muted: #cbd5e1;
    
    --primary: #6366f1; /* Indigo */
    --primary-hover: #4f46e5;
    --secondary: #0ea5e9; /* Light blue */
    --accent: #8b5cf6; /* Violet */
    
    --success: #10b981;
    --error: #ef4444;
    --warning: #f59e0b;
    
    --border: rgba(255, 255, 255, 0.1);
    --glass-border: rgba(255, 255, 255, 0.05);
    
    /* Typography */
    --font-main: 'Cairo', 'Inter', system-ui, sans-serif;
    --font-code: 'JetBrains Mono', 'Fira Code', monospace;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: var(--font-main);
    background: radial-gradient(circle at top right, #1e1b4b, #0b0f19);
    background-attachment: fixed;
    color: var(--text-main);
    line-height: 1.8;
    direction: rtl;
    min-height: 100vh;
}

/* Scrollbar */
::-webkit-scrollbar { width: 10px; }
::-webkit-scrollbar-track { background: var(--bg-main); }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 5px; }
::-webkit-scrollbar-thumb:hover { background: var(--primary); }

/* Typography */
h1, h2, h3, h4 {
    color: var(--text-main);
    margin-bottom: 1.2rem;
    font-weight: 700;
    letter-spacing: -0.5px;
}

p {
    color: var(--text-muted);
    margin-bottom: 1.2rem;
    font-size: 1.15rem;
}

a {
    color: var(--secondary);
    text-decoration: none;
    transition: color 0.3s ease, text-shadow 0.3s ease;
}
a:hover {
    color: var(--primary);
    text-shadow: 0 0 8px rgba(99, 102, 241, 0.5);
}

/* Layout */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem;
}

.header {
    text-align: center;
    margin-bottom: 4rem;
    padding-bottom: 2rem;
    border-bottom: 1px solid var(--border);
    position: relative;
}

.header::after {
    content: '';
    position: absolute;
    bottom: -2px;
    left: 50%;
    transform: translateX(-50%);
    width: 100px;
    height: 3px;
    background: linear-gradient(90deg, var(--primary), var(--secondary));
    border-radius: 3px;
}

.header h1 {
    font-size: 2.6rem;
    background: linear-gradient(to right, #8b5cf6, #3b82f6);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    display: inline-block;
}

.header p {
    font-size: 1.3rem;
    max-width: 800px;
    margin: 0 auto;
}

/* Course Grid */
.course-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: 2.5rem;
}

.lecture-card {
    background: var(--bg-card);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border: 1px solid var(--glass-border);
    border-radius: 16px;
    padding: 2rem;
    transition: all 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
    display: flex;
    flex-direction: column;
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.2);
}
/* replaced above */
.lecture-card h2 { font-size: 1.6rem; margin-bottom: 1rem; }

.lecture-meta {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1.5rem;
    font-size: 0.95rem;
    color: var(--text-muted);
}

.badge {
    background: linear-gradient(135deg, rgba(99, 102, 241, 0.2), rgba(139, 92, 246, 0.2));
    border: 1px solid rgba(99, 102, 241, 0.3);
    padding: 0.3rem 0.8rem;
    border-radius: 9999px;
    font-size: 0.85rem;
    color: #e2e8f0;
}

.progress-bar {
    width: 100%;
    height: 6px;
    background-color: rgba(0,0,0,0.3);
    border-radius: 3px;
    margin-bottom: 2rem;
    overflow: hidden;
}
.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--success), #34d399);
    width: 0%;
    transition: width 0.5s ease-out;
    box-shadow: 0 0 10px rgba(16, 185, 129, 0.5);
}

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    background: linear-gradient(135deg, var(--primary), var(--accent));
    color: white;
    padding: 0.8rem 1.8rem;
    border-radius: 10px;
    font-weight: 700;
    margin-top: auto;
    border: none;
    cursor: pointer;
    font-family: inherit;
    font-size: 1.1rem;
    transition: all 0.3s ease;
    box-shadow: 0 4px 15px rgba(99, 102, 241, 0.3);
}
.btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 25px rgba(99, 102, 241, 0.5);
}

/* ========================================
   LECTURE PAGE STYLES
   ======================================== */

.header-nav {
    pointer-events: none;
}
.header-nav > * {
    pointer-events: auto;

    background: rgba(15, 23, 42, 0.8);
    padding: 1rem 2rem;
    position: sticky;
    top: 0;
    z-index: 100;
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border-bottom: 1px solid rgba(255,255,255,0.1);
    display: flex;
    justify-content: space-between;
    align-items: center;
    box-shadow: 0 4px 20px rgba(0,0,0,0.3);
}

.back-btn {
    color: var(--text-main);
    text-decoration: none;
    display: flex;
    align-items: center;
    gap: 8px;
    font-weight: 600;
    font-size: 1.1rem;
    transition: all 0.3s ease;
    padding: 0.5rem 1rem;
    border-radius: 8px;
    background: rgba(255,255,255,0.05);
}
.back-btn:hover {
    color: var(--primary);
    background: rgba(255,255,255,0.1);
}

.progress-bar-top {
    position: fixed;
    top: 0;
    left: 0;
    height: 4px;
    background: linear-gradient(90deg, var(--primary), var(--secondary));
    width: 0%;
    z-index: 1000;
    transition: width 0.15s ease;
    box-shadow: 0 0 10px var(--primary);
}

/* Slide Container */
.slide-container {
    background: var(--bg-card);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border-radius: 20px;
    padding: 2.5rem;
    margin-bottom: 4rem;
    box-shadow: 0 10px 40px rgba(0, 0, 0, 0.4);
    border: 1px solid var(--glass-border);
    transition: transform 0.4s ease, border-color 0.4s ease;
}
.slide-container:hover {
    border-color: rgba(99, 102, 241, 0.4);
}

.slide-container h2 {
    font-size: 1.5rem;
    color: var(--secondary);
    border-bottom: 2px solid var(--border);
    padding-bottom: 0.8rem;
    margin-bottom: 1.5rem;
}

.slide-image {
    width: 100%;
    max-width: 950px;
    border-radius: 12px;
    margin: 2rem auto;
    display: block;
    box-shadow: 0 10px 30px rgba(0,0,0,0.6);
    border: 1px solid rgba(255,255,255,0.1);
}

/* Explanation Block */
.slide-explanation {
    font-size: 1.2rem;
    line-height: 2;
    color: #e2e8f0;
    margin-top: 2rem;
    padding: 2rem;
    background: rgba(15, 23, 42, 0.5);
    border-radius: 12px;
    border-right: 5px solid var(--primary);
    box-shadow: inset 0 2px 10px rgba(0,0,0,0.2);
}
.slide-explanation p {
    margin-bottom: 1.2rem;
    color: inherit;
}
.slide-explanation strong {
    color: var(--secondary);
    font-weight: 700;
}
.slide-explanation ul, .slide-explanation ol {
    margin-right: 1.5rem;
    margin-bottom: 1.2rem;
}
.slide-explanation li {
    margin-bottom: 0.8rem;
    line-height: 2;
}

/* Inline code in explanations */
.slide-explanation code,
.code-explanation code,
.line-by-line code,
.summary-section code,
.essay-section code {
    font-family: var(--font-code);
    background-color: rgba(99, 102, 241, 0.15);
    padding: 0.15rem 0.5rem;
    border-radius: 4px;
    direction: ltr;
    display: inline-block;
    unicode-bidi: embed;
    color: #c4b5fd;
    font-size: 0.95em;
    border: 1px solid rgba(99, 102, 241, 0.2);
}

/* Block code in explanations */
.slide-explanation pre {
    direction: ltr;
    text-align: left;
    background: #0d1117;
    padding: 1.5rem;
    border-radius: 12px;
    overflow-x: auto;
    font-family: var(--font-code);
    border-left: 5px solid var(--accent);
    margin: 1.5rem 0;
}

/* Code Block Container */
.slide-code {
    background: linear-gradient(135deg, #0d1117, #161b22);
    padding: 1.8rem;
    border-radius: 14px;
    font-family: var(--font-code);
    direction: ltr;
    text-align: left;
    overflow-x: auto;
    margin: 1.5rem 0;
    border: 1px solid rgba(139, 92, 246, 0.25);
    box-shadow: 0 8px 32px rgba(0,0,0,0.5), inset 0 1px 0 rgba(255,255,255,0.05);
    font-size: 0.95rem;
    line-height: 1.75;
    white-space: pre;
    position: relative;
}
.slide-code::before {
    content: 'C++';
    position: absolute;
    top: 8px;
    right: 12px;
    font-size: 0.7rem;
    color: rgba(255,255,255,0.3);
    font-family: var(--font-main);
    text-transform: uppercase;
    letter-spacing: 1px;
}

/* Syntax Highlight Colors */
.keyword { color: #ff7b72; font-weight: bold; }
.type { color: #79c0ff; }
.string { color: #a5d6ff; }
.comment { color: #8b949e; font-style: italic; }
.operator { color: #d2a8ff; }
.number { color: #f2cc60; }
.highlight { color: #fbbf24; font-weight: 700; }

/* Code Explanation Block */
.code-explanation {
    background: rgba(14, 165, 233, 0.08);
    padding: 1.5rem;
    border-radius: 10px;
    margin-top: 1rem;
    border: 1px dashed rgba(14, 165, 233, 0.25);
}
.code-explanation ul { margin-right: 1.5rem; margin-top: 1rem; }
.code-explanation li { margin-bottom: 0.8rem; color: #cbd5e1; line-height: 1.9; }

/* Line-by-line List */
.line-by-line {
    list-style: none;
    margin: 1rem 0;
    padding: 0;
}
.line-by-line li {
    background: rgba(0,0,0,0.2);
    padding: 1rem 1.2rem;
    margin-bottom: 0.8rem;
    border-radius: 10px;
    border-right: 4px solid var(--accent);
    line-height: 1.9;
    color: #e2e8f0;
}

/* Highlight Box */
.highlight-box {
    background: linear-gradient(135deg, rgba(251, 191, 36, 0.08), rgba(245, 158, 11, 0.08));
    border: 1px solid rgba(251, 191, 36, 0.25);
    border-radius: 12px;
    padding: 1.5rem;
    margin: 1.5rem 0;
}

/* ========================================
   QUIZ SECTION
   ======================================== */
.quiz-section {
    background: linear-gradient(145deg, rgba(30,41,59,0.8), rgba(15,23,42,0.9));
    backdrop-filter: blur(10px);
    border-radius: 20px;
    padding: 2.5rem;
    margin: 4rem 0;
    border: 1px solid rgba(14, 165, 233, 0.3);
    box-shadow: 0 15px 35px rgba(0,0,0,0.4);
    direction: ltr;
    text-align: left;
}

.quiz-title {
    color: var(--secondary);
    margin-bottom: 2rem;
    display: flex;
    align-items: center;
    gap: 12px;
    font-size: 1.6rem;
    border-bottom: 1px solid rgba(255,255,255,0.1);
    padding-bottom: 1rem;
}

.question {
    margin-bottom: 2.5rem;
    padding-bottom: 2rem;
    border-bottom: 1px dashed rgba(255,255,255,0.1);
}
.question:last-child {
    border-bottom: none;
    margin-bottom: 0;
    padding-bottom: 0;
}
.question p {
    font-size: 1.15rem;
    font-weight: 600;
    margin-bottom: 1.5rem;
    color: white;
    line-height: 1.7;
}

.options {
    display: flex;
    flex-direction: column;
    gap: 0.8rem;
}

.option-btn {
    background: rgba(255,255,255,0.03);
    border: 1px solid rgba(255,255,255,0.12);
    padding: 1rem 1.2rem;
    border-radius: 10px;
    color: #e2e8f0;
    text-align: left;
    cursor: pointer;
    transition: all 0.25s ease;
    font-family: var(--font-main);
    font-size: 1rem;
}
.option-btn:hover {
    background: rgba(255,255,255,0.08);
    border-color: var(--secondary);
    transform: translateX(5px);
}
.option-btn.correct {
    background: rgba(16, 185, 129, 0.18) !important;
    border-color: #10b981 !important;
    color: #a7f3d0;
    font-weight: bold;
}
.option-btn.wrong {
    background: rgba(239, 68, 68, 0.18) !important;
    border-color: #ef4444 !important;
    color: #fca5a5;
}

.feedback {
    margin-top: 1.2rem;
    padding: 1.2rem;
    border-radius: 10px;
    display: none;
    font-size: 1rem;
    line-height: 1.7;
}
.feedback.show {
    display: block;
    animation: fadeSlideIn 0.5s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

/* ========================================
   SUMMARY SECTION
   ======================================== */
.summary-section {
    background: linear-gradient(145deg, rgba(99, 102, 241, 0.08), rgba(139, 92, 246, 0.08));
    backdrop-filter: blur(10px);
    border-radius: 20px;
    padding: 2.5rem;
    margin: 3rem 0;
    border: 1px solid rgba(99, 102, 241, 0.25);
    box-shadow: 0 10px 30px rgba(0,0,0,0.3);
}
.summary-section h2 {
    color: var(--accent);
    font-size: 1.8rem;
    margin-bottom: 1.5rem;
    display: flex;
    align-items: center;
    gap: 10px;
}
.summary-section ul {
    margin-right: 1rem;
}
.summary-section li {
    margin-bottom: 1rem;
    line-height: 2;
    color: #e2e8f0;
    font-size: 1.1rem;
}
.summary-section li strong {
    color: var(--secondary);
}

/* ========================================
   ESSAY SECTION
   ======================================== */
.essay-section {
    background: linear-gradient(145deg, rgba(16, 185, 129, 0.06), rgba(52, 211, 153, 0.06));
    backdrop-filter: blur(10px);
    border-radius: 20px;
    padding: 2.5rem;
    margin: 3rem 0;
    border: 1px solid rgba(16, 185, 129, 0.25);
    box-shadow: 0 10px 30px rgba(0,0,0,0.3);
}
.essay-section h2 {
    color: var(--success);
    font-size: 1.6rem;
    margin-bottom: 1.5rem;
    display: flex;
    align-items: center;
    gap: 10px;
}

.essay-question {
    background: rgba(0,0,0,0.2);
    padding: 1.5rem;
    border-radius: 12px;
    border-right: 4px solid var(--success);
    margin-bottom: 1.5rem;
    direction: ltr;
    text-align: left;
}
.essay-question p {
    color: white;
    font-weight: 600;
    font-size: 1.15rem;
}

.essay-answer {
    padding: 1.5rem;
    border-radius: 12px;
    background: rgba(16, 185, 129, 0.08);
    border: 1px dashed rgba(16, 185, 129, 0.3);
    direction: ltr;
    text-align: left;
}
.essay-answer h4 {
    color: var(--success);
    margin-bottom: 1rem;
}
.essay-answer p, .essay-answer li {
    color: #d1d5db;
    line-height: 1.9;
    margin-bottom: 0.8rem;
    font-size: 1.05rem;
}
.essay-answer .slide-code {
    margin: 1rem 0;
}

/* Toggle Button for Essay Answer */
.toggle-answer-btn {
    background: linear-gradient(135deg, var(--success), #34d399);
    color: white;
    border: none;
    padding: 0.7rem 1.5rem;
    border-radius: 10px;
    cursor: pointer;
    font-family: inherit;
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 1rem;
    transition: all 0.3s ease;
    display: inline-flex;
    align-items: center;
    gap: 8px;
}
.toggle-answer-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(16, 185, 129, 0.4);
}
.essay-answer.hidden {
    display: none;
}

/* ========================================
   EXAM QUESTION TYPES (Final Exam Format)
   ======================================== */

/* TYPE 2: What is the Output? */
.output-question-section {
    background: linear-gradient(145deg, rgba(6, 182, 212, 0.08), rgba(8, 145, 178, 0.12));
    border: 1px solid rgba(6, 182, 212, 0.3);
    border-radius: 20px;
    padding: 2.5rem;
    margin: 3rem 0;
    direction: ltr;
    text-align: left;
}
.output-question-section h2 {
    color: #22d3ee;
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 2rem;
    font-size: 1.5rem;
    border-bottom: 1px solid rgba(6, 182, 212, 0.2);
    padding-bottom: 1rem;
}
.output-q {
    margin-bottom: 2.5rem;
    padding-bottom: 2rem;
    border-bottom: 1px dashed rgba(6, 182, 212, 0.15);
}
.output-q:last-child {
    border-bottom: none;
    margin-bottom: 0;
    padding-bottom: 0;
}
.output-q > p {
    font-weight: 600;
    color: white;
    margin-bottom: 1rem;
    font-size: 1.1rem;
}
.output-q .slide-code {
    margin-bottom: 1rem;
}
.output-q .reveal-answer {
    background: linear-gradient(135deg, #06b6d4, #0891b2);
}
.output-q .answer-box {
    background: rgba(6, 182, 212, 0.1);
    border: 1px dashed rgba(6, 182, 212, 0.3);
    border-radius: 12px;
    padding: 1.2rem;
    margin-top: 0.8rem;
    font-family: 'JetBrains Mono', monospace;
    color: #67e8f9;
    font-size: 1.05rem;
}
.output-q .answer-box.hidden {
    display: none;
}

/* TYPE 3: Write a Line of Code */
.write-code-section {
    background: linear-gradient(145deg, rgba(245, 158, 11, 0.08), rgba(217, 119, 6, 0.12));
    border: 1px solid rgba(245, 158, 11, 0.3);
    border-radius: 20px;
    padding: 2.5rem;
    margin: 3rem 0;
    direction: ltr;
    text-align: left;
}
.write-code-section h2 {
    color: #fbbf24;
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 2rem;
    font-size: 1.5rem;
    border-bottom: 1px solid rgba(245, 158, 11, 0.2);
    padding-bottom: 1rem;
}
.write-q {
    margin-bottom: 2.5rem;
    padding-bottom: 2rem;
    border-bottom: 1px dashed rgba(245, 158, 11, 0.15);
}
.write-q:last-child {
    border-bottom: none;
    margin-bottom: 0;
    padding-bottom: 0;
}
.write-q > p {
    font-weight: 600;
    color: white;
    margin-bottom: 1rem;
    font-size: 1.1rem;
    line-height: 1.8;
}
.write-q .reveal-answer {
    background: linear-gradient(135deg, #f59e0b, #d97706);
}
.write-q .answer-box {
    background: rgba(245, 158, 11, 0.08);
    border: 1px dashed rgba(245, 158, 11, 0.3);
    border-radius: 12px;
    padding: 1.2rem;
    margin-top: 0.8rem;
}
.write-q .answer-box.hidden {
    display: none;
}

/* TYPE 4: Code Analysis (Based on the following code) */
.code-analysis-section {
    background: linear-gradient(145deg, rgba(244, 63, 94, 0.08), rgba(225, 29, 72, 0.12));
    border: 1px solid rgba(244, 63, 94, 0.3);
    border-radius: 20px;
    padding: 2.5rem;
    margin: 3rem 0;
    direction: ltr;
    text-align: left;
}
.code-analysis-section h2 {
    color: #fb7185;
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 2rem;
    font-size: 1.5rem;
    border-bottom: 1px solid rgba(244, 63, 94, 0.2);
    padding-bottom: 1rem;
}
.code-analysis-section > .slide-code {
    margin-bottom: 2rem;
}
.analysis-q {
    margin-bottom: 2rem;
    padding-bottom: 1.5rem;
    border-bottom: 1px dashed rgba(244, 63, 94, 0.15);
}
.analysis-q:last-child {
    border-bottom: none;
    margin-bottom: 0;
    padding-bottom: 0;
}
.analysis-q > p {
    font-weight: 600;
    color: white;
    margin-bottom: 1rem;
    font-size: 1.1rem;
    line-height: 1.8;
}
.analysis-q .reveal-answer {
    background: linear-gradient(135deg, #f43f5e, #e11d48);
}
.analysis-q .answer-box {
    background: rgba(244, 63, 94, 0.08);
    border: 1px dashed rgba(244, 63, 94, 0.3);
    border-radius: 12px;
    padding: 1.2rem;
    margin-top: 0.8rem;
    color: #fda4af;
    line-height: 1.8;
}
.analysis-q .answer-box.hidden {
    display: none;
}

/* Shared Reveal Button */
.reveal-answer {
    color: white;
    border: none;
    padding: 0.6rem 1.3rem;
    border-radius: 8px;
    cursor: pointer;
    font-family: inherit;
    font-size: 0.95rem;
    font-weight: 600;
    transition: all 0.3s ease;
    display: inline-flex;
    align-items: center;
    gap: 8px;
}
.reveal-answer:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 18px rgba(0,0,0,0.3);
}

/* ========================================
   ENTRANCE ANIMATIONS
   ======================================== */
.animate-target {
    opacity: 0;
    transform: translateY(40px);
    transition: opacity 0.7s ease, transform 0.7s ease;
}
.animate-in {
    opacity: 1;
    transform: translateY(0);
}

@keyframes fadeSlideIn {
    from { opacity: 0; transform: translateY(-10px); }
    to { opacity: 1; transform: translateY(0); }
}

/* ========================================
   PROGRESS TRACKING
   ======================================== */
.completion-btn {
    background: linear-gradient(135deg, rgba(255,255,255,0.05), rgba(255,255,255,0.01));
    border: 1px solid rgba(255, 255, 255, 0.1);
    backdrop-filter: blur(10px);
    color: #e2e8f0;
    padding: 1rem 2rem;
    font-size: 1.1rem;
    font-family: 'Cairo', sans-serif;
    font-weight: 700;
    border-radius: 12px;
    cursor: pointer;
    transition: all 0.3s ease;
    display: inline-flex;
    align-items: center;
    gap: 10px;
    box-shadow: 0 4px 15px rgba(0,0,0,0.2);
}
.completion-btn:hover {
    background: linear-gradient(135deg, rgba(16, 185, 129, 0.15), rgba(16, 185, 129, 0.05));
    border-color: rgba(16, 185, 129, 0.5);
    transform: translateY(-3px);
    box-shadow: 0 8px 25px rgba(16, 185, 129, 0.2);
}
.completion-btn.completed {
    background: linear-gradient(135deg, rgba(16, 185, 129, 0.2), rgba(16, 185, 129, 0.1));
    border-color: #10b981;
    color: #34d399;
}
.lecture-card.completed-card {
    border-color: rgba(16, 185, 129, 0.4);
    box-shadow: 0 0 20px rgba(16, 185, 129, 0.15);
}
.lecture-card.completed-card .badge {
    background: rgba(16, 185, 129, 0.2);
    color: #34d399;
    border: 1px solid rgba(16, 185, 129, 0.3);
}

/* ========================================
   RESPONSIVE
   ======================================== */
@media (max-width: 768px) {
    .container { padding: 1rem; }
    .header h1 { font-size: 1.8rem; }
    .slide-container { padding: 1.5rem; }
    .slide-code { padding: 1rem; font-size: 0.85rem; }
    .quiz-section { padding: 1.5rem; }
    .header-nav {
    pointer-events: none;
}
.header-nav > * {
    pointer-events: auto;
 flex-direction: column; gap: 0.5rem; }
    .summary-section, .essay-section { padding: 1.5rem; }
}


/* --- PREMIUM CSS EFFECTS INJECTED --- */
@keyframes gradientBG {
    0% { background-position: 0% 50%; }
    50% { background-position: 100% 50%; }
    100% { background-position: 0% 50%; }
}

body {
    background: linear-gradient(-45deg, #0b0f19, #1e1b4b, #111827, #312e81);
    background-size: 400% 400%;
    animation: gradientBG 15s ease infinite;
}

.lecture-card {
    position: relative;
    overflow: hidden;
    transition: all 0.5s cubic-bezier(0.25, 0.8, 0.25, 1);
}

.lecture-card::before {
    content: '';
    position: absolute;
    top: 0; left: -100%;
    width: 50%; height: 100%;
    background: linear-gradient(to right, rgba(255,255,255,0) 0%, rgba(255,255,255,0.1) 50%, rgba(255,255,255,0) 100%);
    transform: skewX(-25deg);
    animation: shine 6s infinite;
}

@keyframes shine {
    0% { left: -100%; }
    20% { left: 200%; }
    100% { left: 200%; }
}

.lecture-card:hover {
    transform: translateY(-4px); /* Very subtle */
    box-shadow: 0 10px 30px rgba(99, 102, 241, 0.3), 0 0 15px rgba(139, 92, 246, 0.3) inset;
    border-color: #a78bfa;
}

h1 {
    text-transform: uppercase;
    letter-spacing: 2px;
    background: linear-gradient(270deg, #3b82f6, #8b5cf6, #ec4899, #3b82f6);
    background-size: 800% 800%;
    animation: rainbowText 8s ease infinite;
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    text-shadow: 0 0 20px rgba(139, 92, 246, 0.3);
}

@keyframes rainbowText {
    0% { background-position: 0% 50% }
    50% { background-position: 100% 50% }
    100% { background-position: 0% 50% }
}

.sheet-section {
    transition: all 0.4s ease;
}

.sheet-section:hover {
    box-shadow: 0 15px 40px rgba(52, 211, 153, 0.2), inset 0 0 15px rgba(52, 211, 153, 0.1);
    transform: translateY(-5px);
    border-color: rgba(52, 211, 153, 0.5);
}

.btn {
    position: relative;
    overflow: hidden;
    z-index: 1;
}

.btn::after {
    content: '';
    position: absolute;
    bottom: 0; left: 0;
    width: 100%; height: 100%;
    background: linear-gradient(135deg, #4f46e5, #7c3aed);
    z-index: -1;
    transition: opacity 0.3s ease;
    opacity: 0;
}

.btn:hover::after {
    opacity: 1;
}

.uml-box {
    box-shadow: inset 0 0 20px rgba(59, 130, 246, 0.3), 0 0 15px rgba(59, 130, 246, 0.2);
    border: 2px solid #3b82f6;
    transition: all 0.3s ease;
}

.uml-box:hover {
    box-shadow: inset 0 0 30px rgba(59, 130, 246, 0.5), 0 0 25px rgba(59, 130, 246, 0.4);
    transform: scale(1.01);
}

pre[class*="language-"] {
    box-shadow: 0 10px 30px rgba(0,0,0,0.5), inset 0 0 10px rgba(255,255,255,0.05);
}

.back-btn {
    box-shadow: 0 0 10px rgba(99, 102, 241, 0.3);
}

.back-btn:hover {
    box-shadow: 0 0 20px rgba(99, 102, 241, 0.6);
}

/* --- MOBILE RESPONSIVENESS & ADVANCED GLASSMORPHISM --- */
@media (max-width: 768px) {
    .container {
        padding: 1rem;
    }
    
    .header h1 {
        font-size: 1.8rem;
    }
    
    .header p {
        font-size: 1rem;
    }
    
    .course-grid {
        grid-template-columns: 1fr;
        gap: 1.5rem;
    }
    
    .lecture-card {
        padding: 1.5rem;
    }
    
    .header-nav {
    pointer-events: none;
}
.header-nav > * {
    pointer-events: auto;

        flex-direction: column;
        gap: 1rem;
        padding: 1rem;
    }
    
    .slide-container {
        padding: 1.5rem;
    }
    
    .slide-explanation {
        padding: 1.2rem;
        font-size: 1.05rem;
    }
    
    pre[class*="language-"] {
        padding: 1rem !important;
        font-size: 0.85rem !important;
    }
}

/* Float animations for floating elements if added */
@keyframes float {
    0% { transform: translateY(0px); }
    50% { transform: translateY(-10px); }
    100% { transform: translateY(0px); }
}

.float-effect {
    animation: float 4s ease-in-out infinite;
}


/* --- STABLE & COOL UI ADDITIONS --- */


.author-badge {
    display: inline-block;
    margin-top: 15px;
    padding: 10px 25px;
    background: rgba(15, 23, 42, 0.6);
    border: 1px solid rgba(139, 92, 246, 0.5);
    border-radius: 50px;
    box-shadow: 0 0 20px rgba(139, 92, 246, 0.4), inset 0 0 10px rgba(139, 92, 246, 0.2);
    backdrop-filter: blur(10px);
    animation: pulse-glow 3s infinite alternate;
}

.author-badge span {
    background: linear-gradient(90deg, #fcd34d, #f59e0b, #fcd34d);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    font-size: 1.5rem;
    font-weight: 800;
    letter-spacing: 1px;
}

@keyframes pulse-glow {
    0% { box-shadow: 0 0 10px rgba(139, 92, 246, 0.2), inset 0 0 5px rgba(139, 92, 246, 0.1); transform: scale(1); }
    100% { box-shadow: 0 0 25px rgba(139, 92, 246, 0.6), inset 0 0 15px rgba(139, 92, 246, 0.3); transform: scale(1.02); }
}

.slide-container:hover {
    transform: none; /* Disable distracting transform on study slides */
    border-color: rgba(99, 102, 241, 0.6);
    box-shadow: 0 10px 40px rgba(99, 102, 241, 0.15);
}


/* FIX PARTICLES BACKGROUND */
html { background: #0b0f19; }
body { background: transparent; }
#particles-js {
    position: fixed;
    width: 100%;
    height: 100%;
    background-color: transparent;
    z-index: 0;
    top: 0;
    left: 0;
    pointer-events: auto;
}