:root {
    --bg-primary: #ffffff;
    --bg-secondary: #f8f9fa;
    --bg-card: rgba(255, 255, 255, 0.95);
    --text-primary: #000000;
    --text-secondary: #4a5568;
    --accent-primary: #667eea;
    --accent-secondary: #764ba2;
    --border-color: rgba(0, 0, 0, 0.1);
    --shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
    --bg-gradient-start: #f5f7fa;
    --bg-gradient-end: #e9ecef;
}

[data-theme="dark"] {
    --bg-primary: #1a1f2e;
    --bg-secondary: #252b3d;
    --bg-card: #2d3548;
    --text-primary: #ffffff;
    --text-secondary: #a8b3cf;
    --border-color: rgba(255, 255, 255, 0.05);
    --shadow: 0 10px 30px rgba(0, 0, 0, 0.5);
    --bg-gradient-start: #1a1f2e;
    --bg-gradient-end: #1a1f2e;
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: linear-gradient(135deg, var(--bg-gradient-start) 0%, var(--bg-gradient-end) 100%);
    color: var(--text-primary);
    min-height: 100vh;
    padding: 2rem;
    transition: all 0.3s ease;
}

.theme-toggle {
    position: fixed;
    top: 2rem;
    right: 2rem;
    width: 50px;
    height: 50px;
    background: var(--bg-card);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    box-shadow: var(--shadow);
    transition: transform 0.3s ease;
    z-index: 1000;
    font-size: 1.5rem;
}

.theme-toggle:hover {
    transform: scale(1.1);
}

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

/* Hero Section - Updated for light background */
.hero {
    text-align: center;
    margin-bottom: 4rem;
}

.hero-title {
    font-size: 4rem;
    font-weight: 800;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: 1rem;
}

[data-theme="dark"] .hero-title {
    background: none;
    -webkit-text-fill-color: #ffffff;
    color: #ffffff;
}

.hero-subtitle {
    font-size: 1.5rem;
    color: #64748b;
}

[data-theme="dark"] .hero-subtitle {
    color: #8b95b0;
}

/* Modern Cards Grid - Streamlit Style */
.cards-grid-modern {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 2rem;
    max-width: 1400px;
    margin: 0 auto;
}

.modern-card {
    background: var(--bg-card);
    border-radius: 24px;
    padding: 3rem 2.5rem;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.07);
    transition: all 0.3s ease;
    text-align: left;
    border: 1px solid var(--border-color);
}

[data-theme="dark"] .modern-card {
    background: var(--bg-card);
    box-shadow: 0 8px 16px rgba(0, 0, 0, 0.4);
}

.modern-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 12px 24px rgba(0, 0, 0, 0.12);
}

.icon-box {
    width: 80px;
    height: 80px;
    border-radius: 20px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 1.5rem;
    font-size: 2.5rem;
}

.matrix-gradient {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
}

.vectors-gradient {
    background: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
}

.identity-gradient {
    background: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
}

.dotproduct-gradient {
    background: linear-gradient(135deg, #43e97b 0%, #38f9d7 100%);
}

.magnitude-gradient {
    background: linear-gradient(135deg, #fa709a 0%, #fee140 100%);
}

.addition-gradient {
    background: linear-gradient(135deg, #30cfd0 0%, #330867 100%);
}

.crossproduct-gradient {
    background: linear-gradient(135deg, #a8edea 0%, #fed6e3 100%);
}

.transpose-gradient {
    background: linear-gradient(135deg, #ffecd2 0%, #fcb69f 100%);
}

.determinant-gradient {
    background: linear-gradient(135deg, #ff9a9e 0%, #fecfef 100%);
}

.inverse-gradient {
    background: linear-gradient(135deg, #fbc2eb 0%, #a6c1ee 100%);
}

.eigen-gradient {
    background: linear-gradient(135deg, #fdcbf1 0%, #e6dee9 100%);
}

.projection-gradient {
    background: linear-gradient(135deg, #f6d365 0%, #fda085 100%);
}

.independence-gradient {
    background: linear-gradient(135deg, #96fbc4 0%, #f9f586 100%);
}

.basis-gradient {
    background: linear-gradient(135deg, #6a11cb 0%, #2575fc 100%);
}

.transform-gradient {
    background: linear-gradient(135deg, #fe8c00 0%, #f83600 100%);
}

.orthogonal-gradient {
    background: linear-gradient(135deg, #52c234 0%, #061700 100%);
}

.rank-gradient {
    background: linear-gradient(135deg, #ffd89b 0%, #19547b 100%);
}

.nullspace-gradient {
    background: linear-gradient(135deg, #e0c3fc 0%, #8ec5fc 100%);
}

.systems-gradient {
    background: linear-gradient(135deg, #ffafbd 0%, #ffc3a0 100%);
}

.gaussian-gradient {
    background: linear-gradient(135deg, #2af598 0%, #009efd 100%);
}

.rref-gradient {
    background: linear-gradient(135deg, #ee0979 0%, #ff6a00 100%);
}

.trace-gradient {
    background: linear-gradient(135deg, #f7971e 0%, #ffd200 100%);
}

.gramschmidt-gradient {
    background: linear-gradient(135deg, #56ab2f 0%, #a8e063 100%);
}

.diag-gradient {
    background: linear-gradient(135deg, #614385 0%, #516395 100%);
}

.colrow-gradient {
    background: linear-gradient(135deg, #02aab0 0%, #00cdac 100%);
}

.lu-gradient {
    background: linear-gradient(135deg, #da22ff 0%, #9733ee 100%);
}

.leastsquares-gradient {
    background: linear-gradient(135deg, #f12711 0%, #f5af19 100%);
}

.changebasis-gradient {
    background: linear-gradient(135deg, #4776e6 0%, #8e54e9 100%);
}

.modern-card-title {
    font-size: 1.75rem;
    font-weight: 700;
    color: #1a202c;
    margin-bottom: 1rem;
}

[data-theme="dark"] .modern-card-title {
    color: #ffffff;
}

.modern-card-description {
    font-size: 1rem;
    color: #64748b;
    line-height: 1.6;
    margin-bottom: 2rem;
}

[data-theme="dark"] .modern-card-description {
    color: #d1d5db;
}

.button-row {
    display: flex;
    gap: 0.75rem;
}

.outline-button {
    flex: 1;
    padding: 0.75rem 1.5rem;
    background: transparent;
    border: 2px solid #667eea;
    border-radius: 12px;
    color: #667eea;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
}

[data-theme="dark"] .outline-button {
    border-color: #5b8def;
    color: #5b8def;
}

.outline-button:hover {
    background: rgba(102, 126, 234, 0.1);
    transform: translateY(-2px);
}

[data-theme="dark"] .outline-button:hover {
    background: rgba(91, 141, 239, 0.15);
}

/* Old Cards Grid - Keep for other pages */
.cards-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
}

.card {
    background: var(--bg-card);
    backdrop-filter: blur(10px);
    border-radius: 20px;
    padding: 2.5rem;
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
    cursor: pointer;
    text-align: center;
}

.card:hover {
    transform: translateY(-10px);
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.2);
}

.card-icon {
    font-size: 3rem;
    margin-bottom: 1rem;
}

.card-title {
    font-size: 1.8rem;
    color: var(--text-primary);
    margin-bottom: 1rem;
}

.card-description {
    color: var(--text-secondary);
    margin-bottom: 2rem;
}

.card-button {
    background: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
    color: white;
    border: none;
    padding: 1rem 2rem;
    border-radius: 12px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: transform 0.2s ease;
    width: 100%;
    margin-bottom: 0.75rem;
}

.card-button:hover {
    transform: scale(1.05);
}

.card-button-secondary {
    background: transparent;
    color: var(--text-primary);
    border: 2px solid var(--accent-primary);
    padding: 0.75rem 1.5rem;
    border-radius: 12px;
    font-size: 0.95rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
    width: 100%;
}

.card-button-secondary:hover {
    background: linear-gradient(135deg, rgba(102, 126, 234, 0.1), rgba(118, 75, 162, 0.1));
    transform: scale(1.02);
}

/* Quiz Styles */
#quiz-container {
    background: var(--bg-card);
    backdrop-filter: blur(10px);
    border-radius: 20px;
    padding: 3rem;
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow);
}

.progress-bar {
    text-align: center;
    font-size: 1.2rem;
    color: var(--accent-primary);
    font-weight: 600;
    margin-bottom: 2rem;
}

.question-card {
    margin: 2rem 0;
}

.question-card h2 {
    color: var(--text-primary);
    margin-bottom: 2rem;
    font-size: 1.5rem;
}

/* Answer Options */
.answer-options {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.option-label {
    display: flex;
    align-items: flex-start;
    padding: 1.5rem;
    background: var(--bg-secondary);
    border-radius: 12px;
    cursor: pointer;
    transition: all 0.3s ease;
    border: 2px solid transparent;
}

.option-label:hover {
    border-color: var(--accent-primary);
    transform: translateX(5px);
}

/* Highlight selected MCQ option */
.option-label:has(input[type="radio"]:checked) {
    border-color: var(--accent-primary);
    background: rgba(102, 126, 234, 0.12);
    transform: translateX(5px);
}

.option-label input[type="radio"] {
    margin-right: 1rem;
    margin-top: 0.2rem;
    width: 20px;
    height: 20px;
    min-width: 20px;
    cursor: pointer;
    accent-color: var(--accent-primary);
}

.option-text {
    color: var(--text-primary);
    font-size: 1.1rem;
}

/* Fill in the blank input */
.answer-input {
    width: 100%;
    padding: 1rem;
    font-size: 1.1rem;
    border-radius: 12px;
    border: 2px solid var(--border-color);
    background: var(--bg-secondary);
    color: var(--text-primary);
    transition: border-color 0.3s ease;
}

.answer-input:focus {
    outline: none;
    border-color: var(--accent-primary);
}

/* Buttons */
.button-group {
    display: flex;
    gap: 1rem;
    margin-top: 2rem;
}

.btn {
    padding: 1rem 2rem;
    border-radius: 12px;
    font-size: 1rem;
    font-weight: 600;
    border: none;
    cursor: pointer;
    transition: transform 0.2s ease;
    flex: 1;
}

.btn:hover {
    transform: scale(1.05);
}

.btn-primary {
    background: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
    color: white;
}

.btn-secondary {
    background: var(--bg-secondary);
    color: var(--text-primary);
    border: 2px solid var(--border-color);
}

/* Results */
.score-display {
    background: linear-gradient(135deg, var(--accent-primary), var(--accent-secondary));
    color: white;
    padding: 3rem;
    border-radius: 20px;
    text-align: center;
    margin-bottom: 2rem;
}

.score-number {
    font-size: 3rem;
    font-weight: 800;
    margin-top: 1rem;
}

.review-item {
    background: var(--bg-secondary);
    padding: 2rem;
    border-radius: 12px;
    margin-bottom: 1rem;
}

.review-item h3 {
    color: var(--text-primary);
    margin-bottom: 1rem;
}

.review-item p {
    color: var(--text-secondary);
    margin: 0.5rem 0;
}

.correct {
    color: #10b981;
    font-weight: 600;
}

.incorrect {
    color: #ef4444;
    font-weight: 600;
}

/* Loading Spinner */
.spinner {
    width: 50px;
    height: 50px;
    border: 4px solid var(--border-color);
    border-top-color: var(--accent-primary);
    border-radius: 50%;
    animation: spin 1s linear infinite;
    margin: 2rem auto;
}

@keyframes spin {
    to {
        transform: rotate(360deg);
    }
}

#loading {
    text-align: center;
    padding: 3rem;
    color: var(--text-primary);
}

/* Learn Page */
.page-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 3rem;
    flex-wrap: wrap;
    gap: 1rem;
}

.page-header h1 {
    color: var(--text-primary);
    font-size: 2.5rem;
}

.learn-content {
    background: var(--bg-card);
    backdrop-filter: blur(10px);
    border-radius: 20px;
    padding: 3rem;
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow);
}

.learn-section {
    margin-bottom: 3rem;
}

.learn-section h2 {
    color: var(--text-primary);
    font-size: 2rem;
    margin-bottom: 2rem;
}

.content-card {
    background: var(--bg-secondary);
    padding: 2rem;
    border-radius: 12px;
    margin-bottom: 2rem;
}

.content-card h3 {
    color: var(--text-primary);
    margin-bottom: 1rem;
}

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

.formula {
    background: rgba(102, 126, 234, 0.1);
    padding: 1rem;
    border-radius: 8px;
    margin: 1rem 0;
    font-family: 'Courier New', monospace;
    color: var(--text-primary);
    border-left: 4px solid var(--accent-primary);
}

/* Topic Cards Grid */
.topics-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 2rem;
    margin-top: 2rem;
}

.topic-card {
    background: var(--bg-card);
    backdrop-filter: blur(10px);
    border-radius: 20px;
    padding: 2rem;
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
    cursor: pointer;
    text-align: center;
}

.topic-card:hover {
    transform: translateY(-10px);
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.2);
}

.topic-icon {
    font-size: 3rem;
    margin-bottom: 1rem;
}

.topic-card h3 {
    color: var(--text-primary);
    font-size: 1.5rem;
    margin-bottom: 1rem;
}

.topic-card p {
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
    line-height: 1.6;
}

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

/* Topic Page Styles */
.topic-content {
    background: var(--bg-card);
    backdrop-filter: blur(10px);
    border-radius: 20px;
    padding: 3rem;
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow);
}

.topic-content h2 {
    color: var(--text-primary);
    font-size: 2rem;
    margin: 2rem 0 1rem 0;
}

.topic-content p {
    color: var(--text-secondary);
    line-height: 1.8;
    margin-bottom: 1.5rem;
    font-size: 1.1rem;
}

.example-box {
    background: var(--bg-secondary);
    padding: 1.5rem;
    border-radius: 12px;
    margin: 1.5rem 0;
    border-left: 4px solid var(--accent-primary);
}

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

.navigation-buttons {
    display: flex;
    gap: 1rem;
    margin-top: 3rem;
    flex-wrap: wrap;
}

/* Responsive */
@media (max-width: 768px) {
    .hero-title {
        font-size: 2.5rem;
    }

    .cards-grid {
        grid-template-columns: 1fr;
    }

    .button-group {
        flex-direction: column;
    }

    .page-header {
        flex-direction: column;
        text-align: center;
    }
}