:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --bg-color: #f8fafc;
    --card-bg: #ffffff;
    --text-main: #1e293b;
    --text-muted: #64748b;
    --border-color: #e2e8f0;
    --openai-color: #10a37f;
    --gdm-color: #4285f4;
    --font-sans: 'Inter', system-ui, -apple-system, sans-serif;
    --font-serif: 'Source Serif 4', Georgia, serif;
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
}

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

body {
    font-family: var(--font-sans);
    background-color: var(--bg-color);
    color: var(--text-main);
    line-height: 1.5;
    -webkit-font-smoothing: antialiased;
}

.app-container {
    max-width: 1400px;
    margin: 0 auto;
    padding: 2rem;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

/* Header */
.main-header {
    text-align: center;
    margin-bottom: 3rem;
}

.header-content h1 {
    font-size: 2.5rem;
    font-weight: 700;
    letter-spacing: -0.025em;
    color: var(--text-main);
    margin-bottom: 0.5rem;
}

.header-content p {
    color: var(--text-muted);
    font-size: 1.125rem;
}

/* Navigation */
.problem-nav {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    gap: 0.75rem;
    margin-top: 2rem;
}

.nav-btn {
    background: white;
    border: 1px solid var(--border-color);
    padding: 0.625rem 1.25rem;
    border-radius: 0.5rem;
    font-family: var(--font-sans);
    font-weight: 500;
    color: var(--text-muted);
    cursor: pointer;
    transition: all 0.2s ease;
    box-shadow: var(--shadow-sm);
}

.nav-btn:hover {
    border-color: var(--primary-color);
    color: var(--primary-color);
    transform: translateY(-1px);
}

.nav-btn.active {
    background: var(--primary-color);
    color: white;
    border-color: var(--primary-color);
    box-shadow: var(--shadow-md);
}

/* Main Content */
.main-content {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: 2rem;
}

/* Cards */
.card {
    background: var(--card-bg);
    border-radius: 1rem;
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow-md);
    padding: 2rem;
}

.intro-card {
    margin-bottom: 2rem;
    border-left: 4px solid var(--primary-color);
}

.intro-card h2 {
    font-size: 1.5rem;
    font-weight: 600;
    margin-bottom: 1.5rem;
    color: var(--text-main);
}

/* Problem Text Styling */
.markdown-body {
    font-family: var(--font-serif);
    font-size: 1.125rem;
    line-height: 1.75;
    color: #334155;
}

.markdown-body p {
    margin-bottom: 1.25rem;
}

.markdown-body h1,
.markdown-body h2,
.markdown-body h3 {
    font-family: var(--font-sans);
    color: var(--text-main);
    margin-top: 2rem;
    margin-bottom: 1rem;
    font-weight: 600;
}

.markdown-body ul,
.markdown-body ol {
    margin-bottom: 1.25rem;
    padding-left: 1.5rem;
}

.markdown-body li {
    margin-bottom: 0.5rem;
}

/* Comparison Grid */
.comparison-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
}

.model-column {
    background: var(--card-bg);
    border-radius: 1rem;
    border: 1px solid var(--border-color);
    box-shadow: var(--shadow-md);
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

.column-header {
    padding: 1.5rem;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    gap: 1rem;
    background: #f8fafc;
    /* subtle header bg */
}

.openai-col {
    border-top: 4px solid var(--openai-color);
}

.gdm-col {
    border-top: 4px solid var(--gdm-color);
}

.column-header h2 {
    font-size: 1.25rem;
    font-weight: 600;
    flex: 1;
}

.badge {
    padding: 0.25rem 0.75rem;
    border-radius: 9999px;
    font-size: 0.875rem;
    font-weight: 600;
}

.score {
    background: #d1fae5;
    color: #065f46;
}

.solution-body {
    padding: 2rem;
    font-size: 1.05rem;
    /* Slightly smaller than problem text */
}

/* Footer */
.main-footer {
    margin-top: 4rem;
    text-align: center;
    color: var(--text-muted);
    font-size: 0.875rem;
}

/* Responsive */
@media (max-width: 1024px) {
    .comparison-grid {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 640px) {
    .app-container {
        padding: 1rem;
    }

    .header-content h1 {
        font-size: 1.875rem;
    }
}

/* KaTeX Overrides for consistency */
.katex {
    font-size: 1em !important;
}
/* FAQ Section */
.faq-section {
    margin-top: 3rem;
}

.faq-item {
    margin-bottom: 2rem;
    padding-bottom: 1.5rem;
    border-bottom: 1px solid var(--border-color);
}

.faq-item:last-child {
    margin-bottom: 0;
    padding-bottom: 0;
    border-bottom: none;
}

.faq-item h3 {
    font-size: 1.15rem;
    font-weight: 600;
    color: var(--text-main);
    margin-bottom: 0.5rem;
    font-family: var(--font-sans);
}

.faq-item p {
    color: #475569;
    font-size: 1rem;
    line-height: 1.6;
}

/* Collapsible FAQ Styling */
details.faq-item {
    margin-bottom: 1rem;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 1rem;
    cursor: pointer;
}

details.faq-item:last-child {
    border-bottom: none;
}

summary {
    font-size: 1.15rem;
    font-weight: 600;
    color: var(--text-main);
    font-family: var(--font-sans);
    list-style: none; /* Hide default triangle */
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.5rem 0;
}

summary::-webkit-details-marker {
    display: none;
}

summary::after {
    content: '+';
    font-size: 1.5rem;
    font-weight: 400;
    color: var(--text-muted);
    transition: transform 0.2s;
}

details[open] summary::after {
    transform: rotate(45deg);
}

details[open] summary {
    margin-bottom: 0.5rem;
}

details.faq-item p {
    color: #475569;
    font-size: 1rem;
    line-height: 1.6;
    margin-top: 0;
}