:root {
    --bg-top: #eef2ff;
    --bg-bottom: #e0e7ff;
    --surface: #ffffff;
    --text: #000000;
    --muted: #334155;
    --accent: #4f46e5;
    --accent-soft: #e0e7ff;
    --line: #c7d2fe;
    --shadow: 0 12px 30px rgba(49, 46, 129, 0.18);
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    font-family: "Avenir Next", "Hiragino Kaku Gothic ProN", "Hiragino Sans", sans-serif;
    line-height: 1.75;
    color: var(--text);
    background:
        radial-gradient(circle at 8% 10%, #c7d2fe 0%, transparent 38%),
        radial-gradient(circle at 90% 88%, #dbeafe 0%, transparent 42%),
        linear-gradient(165deg, var(--bg-top), var(--bg-bottom));
    min-height: 100vh;
    padding: 32px 16px 48px;
}

.page {
    width: min(900px, 100%);
    margin: 0 auto;
    background: var(--surface);
    border: 1px solid rgba(199, 210, 254, 0.9);
    border-radius: 18px;
    box-shadow: var(--shadow);
    overflow: hidden;
}

.site-header {
    padding: 22px 24px 16px;
    border-bottom: 1px solid var(--line);
    background: linear-gradient(90deg, rgba(224, 231, 255, 0.95), rgba(219, 234, 254, 0.95));
}

.brand {
    margin: 0 0 14px;
    font-size: 15px;
    font-weight: 700;
    letter-spacing: 0.04em;
    color: var(--muted);
}

.nav {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
}

.nav-link {
    display: inline-block;
    text-decoration: none;
    color: #1e1b4b;
    border: 1px solid #a5b4fc;
    border-radius: 999px;
    padding: 8px 14px;
    font-size: 14px;
    font-weight: 600;
    transition: transform 0.18s ease, background-color 0.18s ease, color 0.18s ease;
    background: #ffffff;
}

.nav-link:hover {
    transform: translateY(-1px);
    background: #eef2ff;
}

.nav-link.active {
    background: var(--accent);
    border-color: var(--accent);
    color: #fff;
}

.content {
    padding: 28px 24px 30px;
}

.page-title {
    margin: 0;
    font-size: clamp(24px, 4vw, 36px);
    letter-spacing: 0.01em;
}

.meta {
    margin: 10px 0 26px;
    color: var(--muted);
    font-size: 14px;
}

.section {
    margin-top: 26px;
    padding-top: 6px;
}

.section h2 {
    margin: 0 0 12px;
    font-size: clamp(19px, 3vw, 24px);
    color: #312e81;
}

.section p,
.section li,
.note {
    font-size: 15px;
}

.section ul {
    margin: 12px 0;
    padding-left: 18px;
}

.formula-card {
    border: 1px solid var(--line);
    background: linear-gradient(180deg, #f8faff, #eef2ff);
    border-radius: 14px;
    padding: 18px;
    margin-top: 8px;
}

.formula {
    margin: 0;
    font-size: 17px;
    font-weight: 700;
    color: #312e81;
}

.example-grid {
    display: grid;
    grid-template-columns: repeat(4, minmax(0, 1fr));
    gap: 12px;
    margin-top: 14px;
}

.example-cell {
    border: 1px solid var(--line);
    background: #f8faff;
    border-radius: 10px;
    padding: 12px;
}

.example-label {
    display: block;
    font-size: 12px;
    color: var(--muted);
    margin-bottom: 4px;
}

.example-value {
    font-size: 16px;
    font-weight: 700;
    color: #312e81;
}

.note {
    margin-top: 14px;
    padding: 10px 12px;
    border-left: 3px solid var(--accent);
    background: var(--accent-soft);
    border-radius: 6px;
}

.form-embed {
    margin-top: 12px;
    border: 1px solid var(--line);
    border-radius: 14px;
    overflow: hidden;
    background: #fff;
    box-shadow: 0 8px 20px rgba(49, 46, 129, 0.08);
}

.form-embed iframe {
    display: block;
    width: 100%;
    min-height: 1100px;
    border: 0;
}

.form-link-text {
    margin: 12px 0 0;
}

.external-form-link {
    display: inline-block;
    padding: 10px 14px;
    border-radius: 999px;
    border: 1px solid var(--accent);
    background: var(--accent);
    color: #fff;
    text-decoration: none;
    font-size: 14px;
    font-weight: 700;
    transition: transform 0.18s ease, opacity 0.18s ease;
}

.external-form-link:hover {
    transform: translateY(-1px);
    opacity: 0.92;
}

.site-footer {
    margin-top: 34px;
    padding-top: 16px;
    border-top: 1px solid var(--line);
    color: #334155;
    font-size: 12px;
    text-align: center;
}

@media (max-width: 680px) {
    body {
        padding: 20px 10px 28px;
    }

    .site-header,
    .content {
        padding: 18px 16px;
    }

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

    .form-embed iframe {
        min-height: 1200px;
    }
}