/* ── Premium black/gray theme ─────────────────────────────────────────────── */
:root {
  --bg: #000000;
  --bg-alt: #0d0d0d;
  --card: #141414;
  --card-hover: #1a1a1a;
  --fg: #f2f2f2;
  --fg-muted: #9a9a9a;
  --fg-dim: #6a6a6a;
  --accent: #d4d4d4;
  --border: rgba(255, 255, 255, 0.1);
  --border-strong: rgba(255, 255, 255, 0.22);
  --code-bg: #111111;
  --node-idle: #333333;
  --node-lit: #e8e8e8;
  --shadow: 0 8px 30px rgba(0, 0, 0, 0.6);
}

* { box-sizing: border-box; }

/* ── GitHub link (top right) ─────────────────────────────────────────────── */
.github-link {
  position: fixed;
  top: 1.2rem;
  right: 1.3rem;
  z-index: 50;
  color: var(--fg-muted);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 2.6rem;
  height: 2.6rem;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: rgba(0, 0, 0, 0.5);
  transition: color 0.2s ease, border-color 0.2s ease, transform 0.2s ease;
}
.github-link:hover {
  color: #fff;
  border-color: var(--border-strong);
  transform: translateY(-2px);
}

html, body {
  background: var(--bg);
  color: var(--fg);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  line-height: 1.65;
  margin: 0;
  padding: 0;
  scroll-behavior: smooth;
}

.container { max-width: 1000px; margin: auto; padding: 1.25rem 1.5rem 3rem; }

h1, h2, h3, h4 {
  color: var(--fg);
  font-weight: 700;
  letter-spacing: 0.01em;
  line-height: 1.25;
}
h1 { font-size: clamp(1.9rem, 4.5vw, 3rem); letter-spacing: -0.02em; }
h2 {
  font-size: clamp(1.35rem, 3vw, 1.8rem);
  margin: 2.5rem 0 0.25rem;
  display: flex;
  align-items: baseline;
  gap: 0.6rem;
}
h2 .idx { color: var(--fg-dim); font-size: 0.9rem; font-weight: 500; letter-spacing: 0.15em; }
h3 { font-size: 1.15rem; margin: 1.5rem 0 0.4rem; }
p { color: var(--fg-muted); max-width: 74ch; }

a { color: var(--accent); text-decoration: none; border-bottom: 1px solid transparent; }
a:hover { border-bottom-color: var(--accent); }

code { font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace; font-size: 0.85em; }
pre {
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 0.9rem 1.1rem;
  overflow-x: auto;
  font-size: 0.82rem;
  color: var(--fg-muted);
}
code { background: var(--code-bg); border-radius: 4px; padding: 0.1em 0.35em; }
pre code { background: none; padding: 0; }

img { max-width: 100%; height: auto; }

.lede { font-size: 1.08rem; color: var(--fg-muted); }

/* ── Hero ─────────────────────────────────────────────────────────────────── */
.hero {
  text-align: center;
  padding-top: 4rem;
  padding-bottom: 1rem;
}
.hero .kicker {
  color: var(--fg-dim);
  text-transform: uppercase;
  letter-spacing: 0.35em;
  font-size: 0.75rem;
  margin-bottom: 1rem;
}
.hero h1 { margin: 0 0 1rem; }
.hero p { margin: 0.5rem auto; }
.hero .cta {
  display: inline-flex;
  gap: 0.6rem;
  margin-top: 1.5rem;
  padding: 0.7rem 1.4rem;
  background: var(--card);
  border: 1px solid var(--border-strong);
  border-radius: 999px;
  color: var(--fg);
  font-size: 0.95rem;
  transition: background 0.2s ease, transform 0.2s ease;
}
.hero .cta:hover { background: var(--card-hover); transform: translateY(-2px); border-bottom-color: var(--border-strong); }

/* ── How it works: 3 steps ───────────────────────────────────────────────── */
.flow {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1rem;
  margin: 1.75rem 0;
}
.flow-step {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 1.4rem 1.25rem;
  transition: border-color 0.25s ease, transform 0.25s ease;
}
.flow-step:hover { border-color: var(--border-strong); transform: translateY(-3px); }
.flow-step .num {
  font-size: 0.72rem;
  letter-spacing: 0.2em;
  color: var(--fg-dim);
  text-transform: uppercase;
}
.flow-step h3 { margin: 0.5rem 0 0.35rem; color: var(--fg); }
.flow-step p { font-size: 0.93rem; margin: 0; }

/* ── Benefit cards ───────────────────────────────────────────────────────── */
.benefits { display: grid; gap: 1.25rem; margin: 1.75rem 0; }
.benefit {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 1.5rem 1.6rem;
  transition: border-color 0.25s ease, box-shadow 0.25s ease;
}
.benefit:hover { border-color: var(--border-strong); box-shadow: var(--shadow); }
.benefit h3 { margin-top: 0; font-size: 1.25rem; display: flex; align-items: center; gap: 0.6rem; }
.benefit .why { color: var(--fg); font-weight: 600; }
.example {
  background: var(--bg-alt);
  border-left: 3px solid var(--accent);
  border-radius: 8px;
  padding: 0.9rem 1.1rem;
  margin: 0.9rem 0;
  font-size: 0.95rem;
  color: var(--fg-muted);
}
.example .label { font-size: 0.72rem; letter-spacing: 0.18em; text-transform: uppercase; color: var(--fg-dim); }

/* ── Read more (collapsible) ─────────────────────────────────────────────── */
details.read-more {
  margin-top: 0.9rem;
  border: 1px solid var(--border);
  border-radius: 12px;
  background: var(--bg-alt);
  overflow: hidden;
}
details.read-more > summary {
  cursor: pointer;
  list-style: none;
  padding: 0.85rem 1.1rem;
  color: var(--fg);
  font-weight: 600;
  font-size: 0.95rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  user-select: none;
  transition: background 0.2s ease;
}
details.read-more > summary::-webkit-details-marker { display: none; }
details.read-more > summary:hover { background: var(--card-hover); }
details.read-more > summary::after {
  content: "+";
  font-size: 1.3rem;
  color: var(--fg-dim);
  transition: transform 0.25s ease;
}
details.read-more[open] > summary::after { transform: rotate(45deg); }
details.read-more > .body { padding: 0.2rem 1.1rem 1.1rem; }
details.read-more .body p { font-size: 0.95rem; }

/* What / Where / Why explanation blocks */
.explain {
  display: grid;
  gap: 0.5rem;
  margin: 0.75rem 0;
}
.explain .row { display: grid; grid-template-columns: 92px 1fr; gap: 0.75rem; align-items: baseline; }
.explain .tag {
  font-size: 0.72rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--fg-dim);
  padding-top: 0.15rem;
}
.explain .txt { color: var(--fg-muted); font-size: 0.95rem; }

.formula {
  background: var(--code-bg);
  border-left: 3px solid var(--accent);
  border-radius: 8px;
  padding: 0.8rem 1rem;
  overflow-x: auto;
  margin: 0.9rem 0;
  font-size: 1.05rem;
  color: var(--fg);
}
.katex-inline { overflow-x: auto; display: inline-block; max-width: 100%; vertical-align: middle; }

/* ── React Flow walkthrough (advanced) ───────────────────────────────────── */
.wt-stage {
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.25rem;
  margin-top: 1rem;
}

.flow-root { display: flex; flex-direction: column; gap: 1rem; }
.flow-toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  flex-wrap: wrap;
}
.flow-counter {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--fg);
  letter-spacing: 0.02em;
}
.flow-btns { display: flex; gap: 0.5rem; flex-wrap: wrap; }

.flow-canvas {
  height: 380px;
  border: 1px solid var(--border);
  border-radius: 12px;
  background: #000;
  overflow: hidden;
  position: relative;
}
.flow-canvas .react-flow__attribution {
  background: transparent;
  color: var(--fg-dim);
}
.flow-canvas .react-flow__attribution a { color: var(--fg-dim); }

.flow-tip {
  position: absolute;
  left: 12px;
  bottom: 12px;
  z-index: 5;
  background: rgba(20, 20, 20, 0.92);
  border: 1px solid var(--border-strong);
  color: var(--fg);
  border-radius: 8px;
  padding: 0.45rem 0.75rem;
  font-size: 0.85rem;
  max-width: 80%;
  pointer-events: none;
}
.flow-tip strong { color: var(--accent); }

.flow-detail {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.1rem 1.25rem;
}
.flow-detail-num {
  font-size: 0.72rem;
  letter-spacing: 0.22em;
  color: var(--fg-dim);
  text-transform: uppercase;
}
.flow-detail-title { font-size: 1.35rem; font-weight: 700; color: var(--fg); margin: 0.2rem 0 0.3rem; }
.flow-detail p { margin: 0; font-size: 1rem; }

.btn {
  background: var(--card);
  color: var(--fg);
  border: 1px solid var(--border-strong);
  padding: 0.5rem 1.1rem;
  border-radius: 999px;
  cursor: pointer;
  font-size: 0.95rem;
  transition: background 0.2s ease, transform 0.12s ease;
}
.btn:hover { background: var(--card-hover); }
.btn:disabled { opacity: 0.4; cursor: not-allowed; transform: none; }
.btn-primary { background: var(--accent); color: #000; border-color: var(--accent); font-weight: 600; }
.btn-primary:hover { background: #fff; }

@media (prefers-reduced-motion: reduce) {
  .flow-step, .benefit { transition: none; }
}

/* ── Gallery (aligned) ───────────────────────────────────────────────────── */
.gallery {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(380px, 1fr));
  gap: 1.5rem;
  margin: 1.5rem 0;
}
.gallery figure {
  margin: 0;
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 0.75rem;
  display: flex;
  flex-direction: column;
}
.gallery .img-wrap {
  aspect-ratio: 4 / 3;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
  background: #000;
  border-radius: 10px;
}
.gallery img { max-width: 100%; max-height: 100%; object-fit: contain; border: none; }
.gallery figcaption { color: var(--fg-muted); font-size: 0.87rem; margin-top: 0.6rem; padding: 0 0.25rem; }

#skillChart { max-width: 100%; margin-top: 1.5rem; }

/* ── Evaluation ──────────────────────────────────────────────────────────── */
.eval-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); gap: 1rem; margin-top: 1.25rem; }
.eval-card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 1.1rem;
  text-align: center;
}
.eval-card .metric { font-size: 1.9rem; font-weight: 800; color: var(--fg); }
.eval-card .label { color: var(--fg-muted); font-size: 0.82rem; margin-top: 0.3rem; }

/* ── Footer ──────────────────────────────────────────────────────────────── */
footer { border-top: 1px solid var(--border); margin-top: 3rem; }
footer p { color: var(--fg-dim); font-size: 0.9rem; }

/* ── Image lightbox (zoom) ──────────────────────────────────────────────── */
.lightbox {
  position: fixed;
  inset: 0;
  z-index: 100;
  background: rgba(0, 0, 0, 0.92);
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.25s ease, visibility 0.25s ease;
}
.lightbox.open { opacity: 1; visibility: visible; }
.lightbox img {
  max-width: 90vw;
  max-height: 88vh;
  object-fit: contain;
  transform-origin: center;
  transition: transform 0.15s ease;
  box-shadow: 0 10px 60px rgba(0, 0, 0, 0.8);
}
.lightbox-close {
  position: absolute;
  top: 1.2rem;
  right: 1.4rem;
  background: none;
  border: 1px solid var(--border-strong);
  color: #fff;
  font-size: 1.3rem;
  width: 2.4rem;
  height: 2.4rem;
  border-radius: 50%;
  cursor: pointer;
  z-index: 2;
  transition: background 0.2s ease;
}
.lightbox-close:hover { background: rgba(255, 255, 255, 0.15); }
.lightbox-controls {
  position: absolute;
  bottom: 1.4rem;
  left: 50%;
  transform: translateX(-50%);
  display: flex;
  gap: 0.5rem;
}
.lightbox-btn {
  background: rgba(255, 255, 255, 0.1);
  border: 1px solid var(--border-strong);
  color: #fff;
  font-size: 1.2rem;
  width: 2.6rem;
  height: 2.6rem;
  border-radius: 50%;
  cursor: pointer;
  transition: background 0.2s ease;
}
.lightbox-btn:hover { background: rgba(255, 255, 255, 0.25); }

@media (max-width: 600px) {
  .explain .row { grid-template-columns: 1fr; gap: 0.1rem; }
  .gallery { grid-template-columns: 1fr; }
}