/* ゼロから始めるKKT 共通スタイル */

:root {
    --c-toshi: #9C27B0;
    --c-toshi-soft: #9C27B022;
    --c-toshi-line: #9C27B044;
    --c-kaikei: #1976D2;
    --c-keizai: #388E3C;
    --c-text: #222;
    --c-muted: #6b7280;
    --c-border: #e5e7eb;
    --c-bg: #ffffff;
    --c-bg-alt: #f8f9fa;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Hiragino Sans",
        "Hiragino Kaku Gothic ProN", "Yu Gothic", Meiryo, sans-serif;
    color: var(--c-text);
    line-height: 1.75;
    background: #fafbfc;
    margin: 0;
    padding: 0;
    font-size: 16px;
}

.container {
    max-width: 900px;
    margin: 0 auto;
    padding: 1.5rem;
}

.site-header {
    background: white;
    border-bottom: 1px solid var(--c-border);
    padding: 0.8rem 1.5rem;
    position: sticky;
    top: 0;
    z-index: 100;
    box-shadow: 0 1px 2px rgba(0,0,0,.04);
}

.site-header .inner {
    max-width: 1000px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.site-header .brand {
    font-weight: 800;
    color: var(--c-toshi);
    text-decoration: none;
    font-size: 1.05rem;
}

.site-header nav a {
    color: var(--c-text);
    text-decoration: none;
    margin-left: 1.2rem;
    font-size: 0.92rem;
    font-weight: 600;
}

.site-header nav a:hover { color: var(--c-toshi); }

.breadcrumb {
    color: var(--c-muted);
    font-size: .85rem;
    margin-bottom: 1rem;
}

.breadcrumb a { color: var(--c-toshi); text-decoration: none; }
.breadcrumb a:hover { text-decoration: underline; }
.breadcrumb .sep { margin: 0 .45rem; color: #cbd5e1; }

.chapter-hero {
    background: linear-gradient(135deg, var(--c-toshi-soft) 0%, #ffffff 100%);
    border-left: 4px solid var(--c-toshi);
    padding: 1.4rem 1.8rem;
    border-radius: 0 10px 10px 0;
    margin-bottom: 2rem;
}

.chapter-hero .tag {
    color: var(--c-toshi);
    font-size: .85rem;
    font-weight: 700;
    letter-spacing: .05em;
}

.chapter-hero h1 {
    margin: .3rem 0 .2rem;
    font-size: 1.55rem;
    letter-spacing: -0.02em;
}

.chapter-hero .subtitle {
    color: var(--c-muted);
    font-size: .95rem;
    margin: 0;
}

h2 {
    color: var(--c-toshi);
    border-left: 6px solid var(--c-toshi);
    padding: .2rem 0 .2rem .8rem;
    margin-top: 2.4rem;
    margin-bottom: 1rem;
    font-size: 1.3rem;
}

h3 {
    color: #333;
    border-bottom: 2px solid var(--c-toshi-soft);
    padding-bottom: .3rem;
    margin-top: 1.8rem;
    margin-bottom: .8rem;
    font-size: 1.12rem;
}

h4 {
    color: #333;
    margin-top: 1.4rem;
    margin-bottom: .5rem;
    font-size: 1rem;
}

p { margin: .9rem 0; }

.lead {
    font-size: 1.02rem;
    color: #444;
    background: var(--c-bg-alt);
    padding: 1rem 1.2rem;
    border-radius: 8px;
    border-left: 3px solid var(--c-toshi);
}

.formula-box {
    background: #f8f9fa;
    border: 1px solid var(--c-border);
    border-radius: 8px;
    padding: 1rem 1.3rem;
    margin: 1rem 0;
    overflow-x: auto;
}

.formula-box .label {
    display: inline-block;
    background: var(--c-toshi);
    color: white;
    font-size: .72rem;
    font-weight: 700;
    padding: .15rem .55rem;
    border-radius: 4px;
    margin-bottom: .4rem;
    letter-spacing: .05em;
}

.key-point {
    background: #fff8e1;
    border-left: 4px solid #f59e0b;
    padding: .85rem 1.2rem;
    margin: 1.1rem 0;
    border-radius: 0 6px 6px 0;
}

.key-point::before {
    content: '💡 ポイント';
    display: block;
    font-weight: 700;
    color: #b45309;
    margin-bottom: .35rem;
}

.warning-box {
    background: #fef2f2;
    border-left: 4px solid #ef4444;
    padding: .85rem 1.2rem;
    margin: 1.1rem 0;
    border-radius: 0 6px 6px 0;
}

.warning-box::before {
    content: '⚠️ 注意';
    display: block;
    font-weight: 700;
    color: #b91c1c;
    margin-bottom: .35rem;
}

.example-box {
    background: #ecfdf5;
    border-left: 4px solid #10b981;
    padding: .9rem 1.2rem;
    margin: 1.1rem 0;
    border-radius: 0 6px 6px 0;
}

.example-box::before {
    content: '📝 例題';
    display: block;
    font-weight: 700;
    color: #047857;
    margin-bottom: .4rem;
}

.summary-box {
    background: linear-gradient(135deg, #f3e8ff 0%, #ffffff 100%);
    border: 1px solid var(--c-toshi-line);
    border-radius: 10px;
    padding: 1.2rem 1.4rem;
    margin: 1.5rem 0;
}

.summary-box h3 {
    margin-top: 0;
    color: var(--c-toshi);
    border: none;
    padding: 0;
}

.summary-box ul { padding-left: 1.2rem; }
.summary-box li { margin: .35rem 0; }

.exam-focus {
    background: #eff6ff;
    border: 2px dashed #3b82f6;
    padding: 1rem 1.3rem;
    border-radius: 8px;
    margin: 1.2rem 0;
}

.exam-focus h3 {
    color: #1d4ed8;
    margin-top: 0;
    border: none;
    padding: 0;
    font-size: 1rem;
}

table.info-table {
    width: 100%;
    border-collapse: collapse;
    margin: 1rem 0;
    font-size: .94rem;
}

table.info-table th {
    background: var(--c-toshi-soft);
    color: var(--c-toshi);
    padding: .55rem .8rem;
    text-align: left;
    border: 1px solid var(--c-toshi-line);
    font-weight: 700;
}

table.info-table td {
    padding: .55rem .8rem;
    border: 1px solid var(--c-border);
    vertical-align: top;
}

table.info-table tr:nth-child(even) td { background: #fafafa; }

.chapter-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 1rem;
    margin: 1.5rem 0;
}

.chapter-card {
    background: white;
    border: 1px solid var(--c-border);
    border-radius: 10px;
    padding: 1.1rem 1.2rem;
    text-decoration: none;
    color: inherit;
    display: flex;
    gap: 1rem;
    transition: all .15s ease;
}

.chapter-card:hover {
    border-color: var(--c-toshi);
    box-shadow: 0 4px 14px rgba(156,39,176,.15);
    transform: translateY(-2px);
}

.chapter-card .num {
    font-size: 1.5rem;
    font-weight: 900;
    color: var(--c-toshi);
    min-width: 4.5rem;   /* 2桁・3桁（Ch10／Ch11〜12）に対応 */
    line-height: 1.1;
    flex-shrink: 0;
    white-space: nowrap;
}

.chapter-card > div:last-child { min-width: 0; flex: 1; }
.chapter-card .title { font-weight: 700; }
.chapter-card .desc { color: var(--c-muted); font-size: .86rem; margin-top: .25rem; }

.nav-btns {
    display: flex;
    gap: .7rem;
    margin: 2rem 0 1rem;
    flex-wrap: wrap;
}

.btn {
    padding: .55rem 1.2rem;
    border-radius: 6px;
    text-decoration: none;
    font-weight: 600;
    font-size: .94rem;
    border: 1px solid transparent;
    transition: all .15s ease;
    display: inline-block;
}

.btn.prev { background: #f3f4f6; color: #374151; }
.btn.prev:hover { background: #e5e7eb; }
.btn.next { background: var(--c-toshi); color: white; }
.btn.next:hover { filter: brightness(1.05); }
.btn.index { background: white; color: var(--c-toshi); border-color: var(--c-toshi); }
.btn.index:hover { background: var(--c-toshi-soft); }

.footer {
    text-align: center;
    color: var(--c-muted);
    font-size: .85rem;
    padding: 2rem 1rem;
    border-top: 1px solid var(--c-border);
    margin-top: 3rem;
}

.toc {
    background: #fafbfc;
    border: 1px solid var(--c-border);
    border-radius: 8px;
    padding: 1rem 1.3rem;
    margin: 1.2rem 0 2rem;
}

.toc h4 { margin: 0 0 .5rem; color: var(--c-toshi); font-size: .95rem; }
.toc ol { margin: 0; padding-left: 1.2rem; font-size: .92rem; }
.toc ol li { margin: .2rem 0; }
.toc a { color: #374151; text-decoration: none; }
.toc a:hover { color: var(--c-toshi); }

.section-anchor { scroll-margin-top: 70px; }

.muted { color: var(--c-muted); }

blockquote {
    border-left: 3px solid #d1d5db;
    color: #4b5563;
    margin: 1rem 0;
    padding: .2rem 1rem;
    font-style: italic;
}

code {
    background: #eef2ff;
    color: #3730a3;
    padding: .1rem .35rem;
    border-radius: 3px;
    font-size: .92em;
}

@media (max-width: 640px) {
    .container { padding: 1rem; }
    .chapter-hero { padding: 1rem 1.1rem; }
    .chapter-hero h1 { font-size: 1.3rem; }
    h2 { font-size: 1.15rem; }
}