:root {
    --primary: #2563eb;
    --primary-dark: #1d4ed8;
    --secondary: #0f172a;
    --light: #f8fafc;
    --gray: #64748b;
    --success: #10b981;
    --warning: #f59e0b;
    --danger: #ef4444;
    --card-bg: #ffffff;
    --border: #e2e8f0;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

body {
    background: linear-gradient(135deg, #f0f9ff 0%, #e0f2fe 100%);
    color: var(--secondary);
    line-height: 1.6;
    min-height: 100vh;
    padding-bottom: 2rem;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1.5rem;
}

/* Header */
header {
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    color: white;
    padding: 2rem 0;
    margin-bottom: 2rem;
    border-radius: 0 0 20px 20px;
    box-shadow: 0 4px 20px rgba(37, 99, 235, 0.3);
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 1rem;
}

.course-info h1 {
    font-size: 2.5rem;
    margin-bottom: 0.5rem;
    font-weight: 800;
}

.course-info p {
    font-size: 1.1rem;
    opacity: 0.9;
    max-width: 600px;
}

.timer {
    background: rgba(255, 255, 255, 0.2);
    padding: 1rem;
    border-radius: 15px;
    text-align: center;
    min-width: 200px;
}

.timer h3 {
    font-size: 1.1rem;
    margin-bottom: 0.5rem;
}

.time-display {
    font-size: 2rem;
    font-weight: 700;
    font-family: 'Courier New', monospace;
}

/* Layout */
.content-grid {
    display: grid;
    grid-template-columns: 1fr 350px;
    gap: 2rem;
}

@media (max-width: 768px) {
    .content-grid {
        grid-template-columns: 1fr;
    }
}

.main-content {
    background: var(--card-bg);
    border-radius: 20px;
    padding: 2rem;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
    margin-bottom: 2rem;
}

/* Sections */
.section {
    margin-bottom: 2.5rem;
}

.section h2 {
    color: var(--primary);
    margin-bottom: 1.5rem;
    padding-bottom: 0.5rem;
    border-bottom: 3px solid var(--primary);
    font-size: 1.8rem;
}

.section h3 {
    color: var(--primary-dark);
    margin: 1.2rem 0 0.8rem;
    font-size: 1.3rem;
}

/* Components */
.learning-objectives {
    background: #dbeafe;
    padding: 1.5rem;
    border-radius: 15px;
    border-left: 4px solid var(--primary);
}

.learning-objectives ul {
    padding-left: 1.5rem;
}

.learning-objectives li {
    margin-bottom: 0.8rem;
}

.analogy-box {
    background: #f0fdf4;
    border: 2px solid var(--success);
    border-radius: 15px;
    padding: 1.5rem;
    margin: 1.5rem 0;
}

.analogy-box h4 {
    color: var(--success);
    margin-bottom: 0.8rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.practice-examples {
    margin: 1.5rem 0;
}

.example {
    background: #f8fafc;
    border: 2px solid var(--border);
    border-radius: 12px;
    padding: 1.5rem;
    margin-bottom: 1.5rem;
}

.example h4 {
    margin-bottom: 1rem;
    color: var(--primary-dark);
}

pre {
    background: var(--secondary);
    color: white;
    padding: 1.2rem;
    border-radius: 10px;
    overflow-x: auto;
    font-size: 0.95rem;
}

code {
    font-family: 'Courier New', monospace;
}

.tip-box {
    background: #fffbeb;
    border: 2px solid var(--warning);
    border-radius: 12px;
    padding: 1rem;
    margin: 1rem 0;
    display: flex;
    align-items: flex-start;
    gap: 1rem;
}

.tip-box .icon {
    font-weight: bold;
    color: var(--warning);
    font-size: 1.2rem;
    min-width: 20px;
}

.blockquote-info {
    background: #e0f2fe;
    padding: 1rem;
    border-left: 4px solid var(--primary);
    margin: 1.5rem 0;
    font-style: italic;
}

/* Quiz/Verification */
.verification {
    background: #f1f5f9;
    padding: 2rem;
    border-radius: 15px;
    margin: 2rem 0;
}

.verification h2 {
    color: var(--primary);
    margin-bottom: 1.5rem;
    text-align: center;
}

.question {
    background: white;
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    border-radius: 12px;
    border-left: 4px solid var(--primary);
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

.question h3 {
    margin-bottom: 1rem;
    color: var(--secondary);
    font-size: 1.2rem;
}

.options {
    display: grid;
    gap: 0.8rem;
}

.option {
    padding: 0.8rem;
    background: #f8fafc;
    border: 2px solid var(--border);
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s ease;
}

.option:hover {
    background: #dbeafe;
    border-color: var(--primary);
}

.option.selected {
    background: #dbeafe;
    border-color: var(--primary);
    font-weight: 600;
}

.option.correct {
    background: #dcfce7;
    border-color: var(--success);
}

.option.incorrect {
    background: #fee2e2;
    border-color: var(--danger);
}

.feedback {
    margin-top: 1rem;
    padding: 1rem;
    border-radius: 8px;
    display: none;
}

.feedback.show {
    display: block;
}

.feedback.correct {
    background: #dcfce7;
    border: 1px solid var(--success);
    color: #065f46;
}

.feedback.incorrect {
    background: #fee2e2;
    border: 1px solid var(--danger);
    color: #991b1b;
}

.analogy-feedback {
    background: #e0f2fe;
    border: 1px solid var(--primary);
    padding: 1rem;
    border-radius: 8px;
    margin-top: 0.8rem;
    font-style: italic;
}

.submit-btn {
    background: var(--primary);
    color: white;
    border: none;
    padding: 12px 24px;
    border-radius: 8px;
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.2s ease;
    margin-top: 1rem;
    width: 100%;
}

.submit-btn:hover {
    background: var(--primary-dark);
}

.submit-btn:disabled {
    background: var(--gray);
    cursor: not-allowed;
}

.results {
    text-align: center;
    padding: 1.5rem;
    margin-top: 1.5rem;
    border-radius: 12px;
    display: none;
}

.results.show {
    display: block;
}

.results.success {
    background: #dcfce7;
    border: 2px solid var(--success);
}

.results.fail {
    background: #fee2e2;
    border: 2px solid var(--danger);
}

/* Challenge */
.challenge {
    background: linear-gradient(135deg, #1e293b 0%, #0f172a 100%);
    color: white;
    padding: 2rem;
    border-radius: 20px;
    margin: 2rem 0;
}

.challenge h2 {
    color: white;
    border-bottom: 3px solid var(--success);
}

.challenge pre {
    background: #0f172a;
    margin: 1.5rem 0;
}

details {
    margin-top: 1.5rem;
}

summary {
    background: var(--success);
    color: white;
    padding: 0.8rem 1.5rem;
    border-radius: 10px;
    cursor: pointer;
    font-weight: 600;
    margin-bottom: 1rem;
}

details[open] summary {
    border-bottom-left-radius: 0;
    border-bottom-right-radius: 0;
}

.solution-content {
    background: #0f172a;
    padding: 1.5rem;
    border-radius: 0 0 10px 10px;
}

/* Sidebar */
.sidebar {
    background: var(--card-bg);
    border-radius: 20px;
    padding: 2rem;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
    height: fit-content;
}

.sidebar h3 {
    color: var(--primary);
    margin-bottom: 1.5rem;
    text-align: center;
}

.lesson-info {
    margin-bottom: 2rem;
}

.info-item {
    display: flex;
    justify-content: space-between;
    padding: 0.8rem 0;
    border-bottom: 1px solid var(--border);
}

.next-lesson {
    background: #dbeafe;
    padding: 1.5rem;
    border-radius: 15px;
    margin-top: 2rem;
}

.next-lesson h4 {
    color: var(--primary);
    margin-bottom: 0.8rem;
}

.progress-bar {
    height: 8px;
    background: var(--border);
    border-radius: 4px;
    margin: 1.5rem 0;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: var(--success);
    width: 0%; /* Dynamic */
    transition: width 0.3s ease;
}

.career-tip {
    background: #f0f9ff;
    border: 2px solid var(--primary);
    border-radius: 12px;
    padding: 1.2rem;
    margin-top: 1.5rem;
}

.career-tip h4 {
    color: var(--primary);
    margin-bottom: 0.5rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

/* Footer & Navigation Buttons */
footer {
    text-align: center;
    margin-top: 2rem;
    color: var(--gray);
    font-size: 0.9rem;
}

.lesson-navigation {
    display: flex;
    justify-content: space-between;
    margin-top: 2rem;
    gap: 1rem;
}

.nav-btn {
    display: inline-flex;
    align-items: center;
    padding: 10px 20px;
    background: white;
    color: var(--primary);
    text-decoration: none;
    border-radius: 10px;
    border: 2px solid var(--primary);
    font-weight: 600;
    transition: all 0.2s ease;
}

.nav-btn:hover {
    background: var(--primary);
    color: white;
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(37, 99, 235, 0.2);
}

.nav-btn .arrow {
    font-size: 1.2rem;
    line-height: 1;
}

.nav-btn.prev .arrow { margin-right: 8px; }
.nav-btn.next .arrow { margin-left: 8px; }

.nav-btn.home {
    background: var(--gray);
    border-color: var(--gray);
    color: white;
}
.nav-btn.home:hover {
    background: var(--secondary);
    border-color: var(--secondary);
}