:root {
    --primary-color: #6366f1;
    --primary-light: #818cf8;
    --primary-dark: #4f46e5;
    --text-primary: #1e1b4b;
    --text-secondary: #64748b;
    --text-muted: #94a3b8;
    --bg-card: #ffffff;
    --bg-subtle: #f8fafc;
    --border-color: #e8e6df;
    --shadow-lg: 0 8px 24px rgba(30, 27, 75, 0.08);
}

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

body {
    font-family: 'DM Sans', -apple-system, BlinkMacSystemFont, sans-serif;
    font-size: 16px;
    line-height: 1.82;
    color: var(--text-primary);
    background: linear-gradient(135deg, #f8f7f4 0%, #eef2ff 50%, #faf5ff 100%);
    background-attachment: fixed;
    -webkit-font-smoothing: antialiased;
    min-height: 100vh;
}

.container {
    max-width: 940px;
    margin: 0 auto;
    padding: 40px 24px 80px;
}

.blog-header {
    margin-bottom: 28px;
    padding-bottom: 24px;
    border-bottom: 2px solid var(--border-color);
}

.back-link {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    color: var(--primary-color);
    text-decoration: none;
    font-size: 14px;
    font-weight: 500;
    margin-bottom: 18px;
}

.back-link:hover { text-decoration: underline; }

.eyebrow {
    color: var(--primary-color);
    font-size: 0.78rem;
    font-weight: 800;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    margin-bottom: 8px;
}

.blog-header h1 {
    font-family: 'DM Serif Display', serif;
    font-size: 2.45rem;
    line-height: 1.2;
    color: var(--text-primary);
    margin-bottom: 12px;
}

.dek {
    max-width: 760px;
    color: var(--text-secondary);
    font-size: 1.04rem;
    line-height: 1.65;
    margin-bottom: 13px;
}

.blog-meta { color: var(--text-secondary); font-size: 14px; }
.blog-meta a { color: var(--primary-color); text-decoration: none; }
.blog-meta a:hover { text-decoration: underline; }

.series-nav {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 10px;
    margin: 0 0 22px;
}

.series-nav a {
    display: block;
    min-height: 72px;
    padding: 12px 14px;
    color: var(--text-secondary);
    background: rgba(255, 255, 255, 0.72);
    border: 1px solid var(--border-color);
    border-radius: 11px;
    text-decoration: none;
    font-size: 0.82rem;
    line-height: 1.42;
}

.series-nav a strong {
    display: block;
    color: var(--text-primary);
    font-size: 0.9rem;
    margin-bottom: 2px;
}

.series-nav a:hover,
.series-nav a[aria-current="page"] {
    border-color: var(--primary-light);
    background: #eef2ff;
}

.series-nav a[aria-current="page"] strong { color: var(--primary-dark); }

.blog-content {
    background: var(--bg-card);
    border-radius: 16px;
    padding: 50px 46px;
    box-shadow: var(--shadow-lg);
    border: 1px solid var(--border-color);
}

.blog-content h2 {
    font-family: 'DM Serif Display', serif;
    font-size: 1.72rem;
    line-height: 1.3;
    margin-top: 52px;
    margin-bottom: 17px;
    padding-bottom: 8px;
    border-bottom: 1px solid var(--border-color);
}

.blog-content h2:first-child { margin-top: 0; }

.blog-content h3 {
    font-size: 1.16rem;
    color: var(--primary-dark);
    margin: 34px 0 11px;
}

.blog-content p { margin-bottom: 16px; }
.blog-content ul, .blog-content ol { padding-left: 24px; margin-bottom: 18px; }
.blog-content li { margin-bottom: 8px; }
.blog-content a { color: var(--primary-color); }

.toc {
    background: var(--bg-subtle);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 18px 22px;
    margin-bottom: 30px;
}

.toc strong { display: block; margin-bottom: 6px; }
.toc ol { margin: 0; }
.toc li { margin-bottom: 3px; }
.toc a { text-decoration: none; }

.callout,
.derivation,
.pitfall {
    padding: 18px 21px;
    margin: 23px 0;
    border-radius: 0 12px 12px 0;
}

.callout {
    background: linear-gradient(135deg, #eef2ff, #faf5ff);
    border-left: 4px solid var(--primary-color);
}

.derivation {
    background: #f8fafc;
    border-left: 4px solid #0f766e;
}

.pitfall {
    background: #fff7ed;
    border-left: 4px solid #ea580c;
}

.callout > strong,
.derivation > strong,
.pitfall > strong {
    display: block;
    margin-bottom: 6px;
}

.derivation > strong { color: #0f766e; }
.pitfall > strong { color: #c2410c; }

.formula-card {
    position: relative;
    background: var(--bg-subtle);
    border: 1px solid #e0e7ff;
    border-radius: 12px;
    padding: 15px 20px 10px;
    margin: 21px 0;
}

.formula-card .equation-label {
    display: block;
    color: var(--text-muted);
    text-align: right;
    font-size: 0.75rem;
    margin-top: -4px;
}

.equation-label[id] {
    scroll-margin-top: 12rem;
}

.optional-derivation {
    margin: 20px 0 28px;
    border: 1px solid var(--border-color);
    border-radius: 11px;
    background: #fbfcfe;
}

.optional-derivation summary {
    cursor: pointer;
    padding: 13px 16px;
    color: var(--primary-dark);
    font-size: 0.9rem;
    font-weight: 700;
}

.optional-derivation[open] summary {
    border-bottom: 1px solid var(--border-color);
}

.optional-derivation .details-body {
    padding: 2px 16px 12px;
}

.optional-derivation .formula-card {
    margin: 14px 0;
}

.plot-figure {
    margin: 26px 0 30px;
    padding: 14px 14px 12px;
    background: #fbfcfe;
    border: 1px solid var(--border-color);
    border-radius: 13px;
}

.plot-figure canvas {
    display: block;
    width: 100%;
    aspect-ratio: 2.15 / 1;
}

.plot-figure a,
.plot-figure img {
    display: block;
    width: 100%;
    max-width: 100%;
}

.plot-figure img { height: auto; }

.latex-figure {
    width: 100%;
    max-width: 760px;
    margin-left: auto;
    margin-right: auto;
    overflow: hidden;
    background: #fff;
}

.plot-figure figcaption {
    color: var(--text-secondary);
    font-size: 0.82rem;
    line-height: 1.55;
    padding: 7px 5px 0;
}

.concept-figure {
    margin: 27px 0 31px;
    padding: 18px;
    background: #fbfcfe;
    border: 1px solid var(--border-color);
    border-radius: 13px;
}

.concept-figure figcaption {
    color: var(--text-secondary);
    font-size: 0.82rem;
    line-height: 1.55;
    padding-top: 11px;
}

.concept-flow {
    display: grid;
    grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr) auto minmax(0, 1fr) auto minmax(0, 1fr);
    gap: 9px;
    align-items: stretch;
}

.concept-node {
    display: flex;
    flex-direction: column;
    justify-content: center;
    min-height: 112px;
    padding: 13px;
    background: #fff;
    border: 1px solid #dfe4f5;
    border-radius: 10px;
    line-height: 1.4;
}

.concept-node strong {
    font-size: 0.91rem;
    margin: 3px 0 6px;
}

.concept-node > span:last-child {
    color: var(--text-secondary);
    font-size: 0.78rem;
}

.concept-kicker {
    color: var(--primary-dark);
    font-size: 0.68rem;
    font-weight: 800;
    letter-spacing: 0.08em;
    text-transform: uppercase;
}

.concept-arrow {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-width: 41px;
    color: var(--text-muted);
    line-height: 1.15;
}

.concept-arrow span {
    max-width: 58px;
    font-size: 0.64rem;
    text-align: center;
}

.concept-arrow b {
    color: var(--primary-color);
    font-size: 1.25rem;
    font-weight: 500;
}

.method-map {
    display: grid;
    gap: 7px;
}

.method-map-head,
.method-row {
    display: grid;
    grid-template-columns: 105px minmax(0, 1fr) minmax(0, 1.15fr);
    gap: 12px;
    align-items: center;
}

.method-map-head {
    padding: 0 12px 3px;
    color: var(--text-muted);
    font-size: 0.68rem;
    font-weight: 800;
    letter-spacing: 0.06em;
    text-transform: uppercase;
}

.method-row {
    min-height: 58px;
    padding: 10px 12px;
    background: #fff;
    border: 1px solid #e2e8f0;
    border-left: 4px solid var(--primary-light);
    border-radius: 9px;
    line-height: 1.35;
}

.method-name {
    color: var(--primary-dark);
    font-size: 0.89rem;
}

.method-signal {
    font-size: 0.82rem;
    font-weight: 700;
}

.method-note {
    color: var(--text-secondary);
    font-size: 0.78rem;
}

.particle-triptych {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 11px;
}

.particle-panel {
    padding: 12px;
    background: #fff;
    border: 1px solid #e2e8f0;
    border-radius: 10px;
}

.particle-panel > strong,
.particle-panel > span {
    display: block;
    line-height: 1.35;
}

.particle-panel > strong { font-size: 0.88rem; }
.particle-panel > span { color: var(--text-secondary); font-size: 0.72rem; }

.particle-stage {
    position: relative;
    height: 132px;
    margin-top: 9px;
    overflow: hidden;
    border-radius: 8px;
    background:
        linear-gradient(rgba(226, 232, 240, 0.55) 1px, transparent 1px),
        linear-gradient(90deg, rgba(226, 232, 240, 0.55) 1px, transparent 1px),
        #f8fafc;
    background-size: 24px 24px;
}

.particle-dot {
    position: absolute;
    left: var(--x);
    top: var(--y);
    width: 10px;
    height: 10px;
    border-radius: 50%;
    transform: translate(-50%, -50%);
}

.particle-dot.target {
    background: #0f766e;
    box-shadow: 0 0 0 3px rgba(15, 118, 110, 0.12);
}

.particle-dot.model {
    background: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.12);
}

.motion-arrow {
    position: absolute;
    left: var(--x);
    top: var(--y);
    width: var(--w);
    height: 2px;
    color: #475569;
    background: currentColor;
    transform: rotate(var(--r));
    transform-origin: left center;
}

.motion-arrow::after {
    content: "";
    position: absolute;
    right: -1px;
    top: -3px;
    border-top: 4px solid transparent;
    border-bottom: 4px solid transparent;
    border-left: 6px solid currentColor;
}

.particle-legend {
    display: flex;
    flex-wrap: wrap;
    gap: 14px;
    margin-top: 10px;
    color: var(--text-secondary);
    font-size: 0.76rem;
}

.particle-legend span::before {
    content: "";
    display: inline-block;
    width: 8px;
    height: 8px;
    margin-right: 5px;
    border-radius: 50%;
}

.particle-legend .legend-real::before { background: #0f766e; }
.particle-legend .legend-model::before { background: var(--primary-color); }

.legend-swatch {
    display: inline-block;
    width: 18px;
    height: 3px;
    margin: 0 5px 2px 10px;
    border-radius: 999px;
    vertical-align: middle;
}

.legend-swatch:first-child { margin-left: 0; }
.legend-target { background: #0f766e; }
.legend-student { background: #6366f1; }

.step {
    display: grid;
    grid-template-columns: 34px 1fr;
    gap: 12px;
    margin: 24px 0;
}

.step-number {
    display: flex;
    align-items: center;
    justify-content: center;
    width: 30px;
    height: 30px;
    border-radius: 50%;
    background: #e0e7ff;
    color: var(--primary-dark);
    font-size: 0.82rem;
    font-weight: 800;
}

.step-body h3 { margin: 2px 0 7px; }

.table-wrap { overflow-x: auto; margin: 20px 0 26px; }
table { width: 100%; border-collapse: collapse; font-size: 0.88rem; }
th, td {
    padding: 10px 12px;
    border-bottom: 1px solid var(--border-color);
    text-align: left;
    vertical-align: top;
}
th { background: #eef2ff; color: var(--primary-dark); font-weight: 700; }
tbody tr:last-child td { border-bottom: 0; }

code {
    font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
    font-size: 0.88em;
    background: #f1f5f9;
    padding: 0.12em 0.35em;
    border-radius: 4px;
}

.katex-display {
    overflow-x: auto;
    overflow-y: hidden;
    padding: 8px 0;
    margin: 11px 0;
}

.katex { font-size: 1.02em; }

.next-post {
    display: flex;
    justify-content: space-between;
    gap: 18px;
    align-items: center;
    margin-top: 48px;
    padding-top: 24px;
    border-top: 1px solid var(--border-color);
}

.next-post a { font-weight: 700; text-decoration: none; }
.references p { color: var(--text-secondary); font-size: 0.9rem; margin-bottom: 9px; }

@media (max-width: 700px) {
    .container { padding: 24px 16px 60px; }
    .blog-content { padding: 30px 20px; }
    .blog-header h1 { font-size: 1.82rem; }
    .series-nav { grid-template-columns: 1fr; }
    .series-nav a { min-height: 0; }
    .step { grid-template-columns: 28px 1fr; gap: 9px; }
    .step-number { width: 27px; height: 27px; }
    .concept-flow { grid-template-columns: 1fr; }
    .concept-arrow { min-height: 34px; }
    .concept-arrow b { transform: rotate(90deg); }
    .concept-arrow span { max-width: none; }
    .method-map-head { display: none; }
    .method-row { grid-template-columns: 1fr; gap: 3px; }
    .particle-triptych { grid-template-columns: 1fr; }
    .particle-stage { height: 124px; }
    .katex-display { font-size: 0.85em; }
    th, td { padding: 8px; }
    .next-post { align-items: flex-start; flex-direction: column; }
}