:root {
    --bg: #f8fafc;
    --text-main: #0f172a;
    --text-muted: #475569;
    --primary: #4f46e5;
    --primary-hover: #4338ca;
    --primary-light: #eef2ff;
    --card: #ffffff;
    --border: #e2e8f0;
}

* {
    box-sizing: border-box;
}

body {
    font-family: 'Segoe UI', system-ui, -apple-system, Roboto, sans-serif;
    background-color: var(--bg);
    color: var(--text-main);
    margin: 0;
    padding: 0;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    line-height: 1.7;
}

.navbar {
    background: var(--card);
    padding: 14px 24px;
    border-bottom: 1px solid var(--border);
    box-shadow: 0 1px 3px rgba(0,0,0,0.04);
    position: sticky;
    top: 0;
    z-index: 100;
}

.navbar-inner {
    max-width: 1040px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 12px;
}

.brand-logo {
    font-size: 20px;
    font-weight: 700;
    color: var(--primary);
    text-decoration: none;
    display: flex;
    align-items: center;
    gap: 8px;
}

.top-nav {
    display: flex;
    gap: 18px;
    flex-wrap: wrap;
    align-items: center;
}

.top-nav a {
    text-decoration: none;
    color: var(--text-muted);
    font-size: 14px;
    font-weight: 500;
    transition: color 0.2s;
}

.top-nav a:hover, .top-nav a.active {
    color: var(--primary);
}

.btn {
    background: var(--primary);
    color: white;
    border: none;
    padding: 10px 20px;
    border-radius: 8px;
    font-size: 14px;
    font-weight: 600;
    cursor: pointer;
    text-decoration: none;
    display: inline-block;
    transition: background 0.2s;
}

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

.page-container {
    max-width: 920px;
    margin: 40px auto;
    padding: 0 20px;
    flex: 1;
    width: 100%;
}

.paper-card {
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: 12px;
    padding: 44px 48px;
    box-shadow: 0 4px 6px -1px rgba(0,0,0,0.05);
}

.paper-card h1 {
    font-size: 30px;
    color: #0f172a;
    margin-top: 0;
    margin-bottom: 20px;
    border-bottom: 2px solid var(--border);
    padding-bottom: 12px;
}

.paper-card h2 {
    font-size: 21px;
    color: var(--primary);
    margin-top: 30px;
    margin-bottom: 12px;
}

.paper-card h3 {
    font-size: 17px;
    color: #1e293b;
    margin-top: 20px;
    margin-bottom: 8px;
}

.paper-card p, .paper-card li {
    color: var(--text-muted);
}

.paper-card ul, .paper-card ol {
    padding-left: 22px;
    margin-bottom: 16px;
}

.paper-card li {
    margin-bottom: 8px;
}

.math-box {
    background: var(--primary-light);
    border-left: 4px solid var(--primary);
    padding: 16px 20px;
    border-radius: 0 8px 8px 0;
    margin: 16px 0;
    font-family: 'Consolas', 'Cambria Math', serif;
    color: #1e1b4b;
}

.ref-table {
    width: 100%;
    border-collapse: collapse;
    margin: 20px 0;
    font-size: 14px;
}

.ref-table th, .ref-table td {
    border: 1px solid var(--border);
    padding: 12px 14px;
    text-align: left;
}

.ref-table th {
    background: #f1f5f9;
    color: #0f172a;
    font-weight: 700;
}

.site-footer {
    background: #0f172a;
    color: #cbd5e1;
    padding: 40px 24px 28px;
    margin-top: auto;
}

.footer-inner {
    max-width: 960px;
    margin: 0 auto;
    display: flex;
    flex-direction: column;
    gap: 18px;
    align-items: center;
    text-align: center;
}

.footer-links {
    display: flex;
    flex-wrap: wrap;
    gap: 20px;
    justify-content: center;
}

.footer-links a {
    color: #e2e8f0;
    text-decoration: none;
    font-size: 14px;
    font-weight: 500;
}

.footer-links a:hover {
    color: #818cf8;
    text-decoration: underline;
}

.footer-copy {
    font-size: 13px;
    color: #94a3b8;
}

@media (max-width: 768px) {
    .paper-card {
        padding: 24px 20px;
    }
}