:root {
    --bg: #f4f7fb;
    --panel: #ffffff;
    --text: #1f2a44;
    --muted: #60708f;
    --line: #d9e2f2;
    --accent: #4f7cff;
    --accent-soft: rgba(79, 124, 255, 0.12);
    --success: #1f9d72;
    --shadow: 0 18px 50px rgba(42, 64, 108, 0.12);
}

* { box-sizing: border-box; }

body {
    margin: 0;
    font-family: "Microsoft YaHei", "PingFang SC", "Segoe UI", sans-serif;
    color: var(--text);
    background: linear-gradient(180deg, #eef4ff 0%, var(--bg) 240px);
    line-height: 1.7;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

.hero {
    padding: 40px 24px 24px;
    background: radial-gradient(circle at top right, rgba(79,124,255,.18), transparent 32%), transparent;
}

.hero-inner, .main {
    width: min(1100px, calc(100% - 32px));
    margin: 0 auto;
}

.hero h1 {
    margin: 0 0 12px;
    font-size: clamp(30px, 4vw, 44px);
    line-height: 1.2;
}

.hero p {
    margin: 0;
    max-width: 760px;
    color: var(--muted);
    font-size: 16px;
}

.main {
    padding: 24px 0 56px;
    display: grid;
    gap: 20px;
}

.panel {
    background: var(--panel);
    border: 1px solid rgba(217, 226, 242, 0.9);
    border-radius: 20px;
    box-shadow: var(--shadow);
    padding: 24px;
}

.panel h2, .panel h3 { margin-top: 0; }

.panel p:last-child,
.panel ul:last-child,
.panel ol:last-child { margin-bottom: 0; }

.badge {
    display: inline-flex;
    align-items: center;
    gap: 8px;
    padding: 6px 12px;
    border-radius: 999px;
    background: var(--accent-soft);
    color: var(--accent);
    font-weight: 700;
    margin-bottom: 12px;
    font-size: 14px;
}

.chart-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 20px;
}

.chart-card {
    border: 1px solid var(--line);
    border-radius: 18px;
    padding: 18px;
    background: linear-gradient(180deg, rgba(79,124,255,.04), rgba(255,255,255,1));
}

.chart-card h3 { margin-bottom: 8px; }

.chart-shell {
    position: relative;
    height: 360px;
}

.chart-shell.tall { height: 460px; }
.chart-shell.short { height: 240px; }

.tip-list li + li,
.exercise-list li + li,
.learn-list li + li { margin-top: 8px; }

.nav-links {
    display: flex;
    flex-wrap: wrap;
    gap: 12px;
}

.nav-links a {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    min-width: 120px;
    padding: 10px 16px;
    border-radius: 12px;
    border: 1px solid var(--line);
    background: #fff;
    font-weight: 700;
}

.callout {
    padding: 16px 18px;
    border-radius: 16px;
    background: rgba(31, 157, 114, 0.08);
    border: 1px solid rgba(31, 157, 114, 0.18);
}

.cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 16px;
}

.mini-card {
    padding: 18px;
    border-radius: 18px;
    border: 1px solid var(--line);
    background: #fff;
}

.mini-card strong {
    display: block;
    font-size: 28px;
    margin-top: 10px;
}

.button-row {
    display: flex;
    flex-wrap: wrap;
    gap: 12px;
    margin-top: 16px;
}

button {
    border: none;
    border-radius: 12px;
    padding: 10px 14px;
    font: inherit;
    font-weight: 700;
    cursor: pointer;
    background: var(--accent);
    color: #fff;
    box-shadow: 0 10px 24px rgba(79,124,255,.22);
}

button.secondary {
    background: #fff;
    color: var(--text);
    border: 1px solid var(--line);
    box-shadow: none;
}

.course-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
    gap: 16px;
}

.course-card {
    padding: 18px;
    border-radius: 18px;
    border: 1px solid var(--line);
    background: #fff;
    display: block;
    color: inherit;
    transition: transform .18s ease, box-shadow .18s ease;
}

.course-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow);
    text-decoration: none;
}

.course-card .num {
    color: var(--accent);
    font-weight: 800;
    font-size: 14px;
    margin-bottom: 10px;
}

footer {
    color: var(--muted);
    text-align: center;
    padding: 8px 0 24px;
}

table.params {
    width: 100%;
    border-collapse: collapse;
    margin: 12px 0 4px;
    font-size: 14px;
}

table.params th,
table.params td {
    border: 1px solid var(--line);
    padding: 10px 12px;
    text-align: left;
    vertical-align: top;
}

table.params th {
    background: var(--accent-soft);
    color: var(--accent);
    font-weight: 700;
    white-space: nowrap;
}

table.params td code {
    background: rgba(79, 124, 255, 0.08);
    padding: 1px 6px;
    border-radius: 4px;
    font-size: 13px;
}

table.params td:first-child {
    white-space: nowrap;
    font-weight: 700;
    color: var(--text);
}

table.params tr:nth-child(even) td {
    background: rgba(217, 226, 242, 0.18);
}

.toc {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 10px;
}

.toc a {
    display: block;
    padding: 10px 14px;
    border: 1px solid var(--line);
    border-radius: 12px;
    background: #fff;
    font-weight: 700;
}

.toc a:hover {
    background: var(--accent-soft);
    text-decoration: none;
}

.panel h3 { margin-top: 24px; }
.panel h3:first-child { margin-top: 0; }
.small { color: var(--muted); font-size: 13px; }