:root{
  /* Light theme */
  --bg: #f6f7fb;
  --bg2: #eef1f7;

  --card: rgba(255,255,255,0.92);
  --card2: rgba(255,255,255,0.72);

  --text: #0f172a;      /* slate-900 */
  --muted: #334155;     /* slate-700 */
  --muted2: #64748b;    /* slate-500 */

  --border: rgba(15, 23, 42, 0.10);
  --shadow: 0 10px 30px rgba(2, 6, 23, 0.10);

  --radius: 16px;
  --radius2: 12px;

  --mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", "Courier New", monospace;
  --sans: ui-sans-serif, system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, "Apple Color Emoji","Segoe UI Emoji";
}

*{ box-sizing: border-box; }
html, body{ height: 100%; }

body{
  margin: 0;
  font-family: var(--sans);
  color: var(--text);
  background:
    radial-gradient(1200px 600px at 10% -10%, rgba(59,130,246,0.12), transparent 60%),
    radial-gradient(900px 500px at 90% 0%, rgba(168,85,247,0.10), transparent 55%),
    radial-gradient(700px 500px at 50% 120%, rgba(20,184,166,0.10), transparent 60%),
    linear-gradient(180deg, var(--bg), var(--bg2));
}

a{ color: #1d4ed8; text-decoration: none; }
a:hover{ text-decoration: underline; text-underline-offset: 3px; }

.wrap{ max-width: 1080px; margin: 0 auto; padding: 22px 18px 70px; }

/* Header */
.header{
  position: sticky;
  top: 0;
  z-index: 10;
  margin: -22px -18px 18px;
  padding: 12px 18px;
  backdrop-filter: blur(10px);
  background: rgba(246,247,251,0.72);
  border-bottom: 1px solid var(--border);
}

.headerInner{
  max-width: 1080px;
  margin: 0 auto;
  display: flex;
  gap: 14px;
  align-items: center;
  justify-content: space-between;
}

.brand{
  display:flex;
  flex-direction: column;
  gap: 3px;
}
.brandTitle{
  font-weight: 780;
  letter-spacing: -0.2px;
  line-height: 1.1;
  color: var(--text);
}
.brandTitle a{ color: inherit; }
.brandSub{
  color: var(--muted2);
  font-size: 12px;
}

/* Nav pills */
.nav{
  display:flex;
  gap: 10px;
  flex-wrap: wrap;
  justify-content: flex-end;
}
.nav a{
  border: 1px solid var(--border);
  background: rgba(255,255,255,0.75);
  padding: 8px 10px;
  border-radius: 999px;
  font-size: 13px;
  color: var(--muted);
}
.nav a:hover{
  background: rgba(255,255,255,0.95);
  text-decoration: none;
  border-color: rgba(15, 23, 42, 0.16);
}

/* Hero */
.hero{
  border: 1px solid var(--border);
  background: linear-gradient(180deg, rgba(255,255,255,0.95), rgba(255,255,255,0.86));
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 20px 20px 16px;
  position: relative;
  overflow: hidden;
}
.hero:before{
  content:"";
  position:absolute; inset:-2px;
  background: radial-gradient(900px 260px at 12% 0%, rgba(59,130,246,0.10), transparent 62%);
  pointer-events:none;
}
.hero h1{
  margin: 0 0 6px;
  font-size: clamp(24px, 3vw, 40px);
  letter-spacing: -0.6px;
}
.hero p{
  margin: 0;
  color: var(--muted);
  max-width: 90ch;
  line-height: 1.7;
  font-size: 15px;
}

.metaRow{
  display:flex; flex-wrap:wrap; gap: 10px; margin-top: 14px;
}
.tag{
  border: 1px solid var(--border);
  background: rgba(15,23,42,0.03);
  padding: 8px 12px;
  border-radius: 999px;
  color: var(--muted);
  font-size: 13px;
}

/* Grids */
.grid2{
  display:grid;
  grid-template-columns: 1.05fr 0.95fr;
  gap: 18px;
  margin-top: 18px;
}
@media (max-width: 920px){
  .grid2{ grid-template-columns: 1fr; }
  .nav{ justify-content: flex-start; }
}

/* Cards */
.card{
  border: 1px solid var(--border);
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 18px;
}
.card h2{
  margin: 0 0 10px;
  font-size: 18px;
  letter-spacing: -0.2px;
}
.card h3{
  margin: 16px 0 8px;
  font-size: 15px;
  letter-spacing: -0.1px;
}
.card p, .card li{
  color: var(--muted);
  line-height: 1.75;
  font-size: 14px;
}
.hr{
  height: 1px;
  background: rgba(15, 23, 42, 0.10);
  margin: 14px 0;
}

/* Buttons */
.btnRow{ display:flex; flex-wrap:wrap; gap: 10px; margin-top: 10px; }

.btn{
  display:inline-flex; align-items:center; gap: 10px;
  padding: 10px 12px;
  border-radius: 12px;
  border: 1px solid rgba(29, 78, 216, 0.18);
  background: rgba(29, 78, 216, 0.06);
  transition: transform 0.06s ease, background 0.2s ease, border-color 0.2s ease;
  font-size: 14px;
  color: #1d4ed8;
}
.btn:hover{
  background: rgba(29, 78, 216, 0.10);
  border-color: rgba(29, 78, 216, 0.25);
  text-decoration:none;
}
.btn:active{ transform: translateY(1px); }
.btn .small{
  color: var(--muted2);
  font-family: var(--mono);
  font-size: 12px;
}

/* TOC tiles */
.toc{
  display:grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}
@media (max-width: 920px){
  .toc{ grid-template-columns: 1fr; }
}
.toc a{
  display:block;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: rgba(255,255,255,0.86);
  padding: 14px;
  box-shadow: 0 8px 22px rgba(2,6,23,0.06);
}
.toc a:hover{
  background: rgba(255,255,255,0.98);
  text-decoration:none;
  border-color: rgba(15, 23, 42, 0.16);
}
.toc .title{ font-weight: 750; color: var(--text); }
.toc .desc{ color: var(--muted2); font-size: 13px; margin-top: 6px; line-height: 1.55; }

/* Figures */
.figure{
  margin: 14px 0 0;
  border: 1px solid var(--border);
  background: rgba(255,255,255,0.92);
  border-radius: var(--radius2);
  overflow: hidden;
  box-shadow: 0 10px 26px rgba(2,6,23,0.08);
}
.figure img{ width: 100%; height: auto; display:block; }
.figcap{
  padding: 10px 12px 12px;
  border-top: 1px solid rgba(15, 23, 42, 0.10);
  color: var(--muted2);
  font-size: 12.5px;
  line-height: 1.55;
  font-family: var(--mono);
}

/* Key-value blocks */
.kv{
  display:grid;
  grid-template-columns: 60px 1fr;
  gap: 4px 14px;
  margin-top: 10px;
}
@media (max-width: 540px){
  .kv{ grid-template-columns: 1fr; }
}
.k{ color: var(--muted2); font-family: var(--mono); font-size: 12.5px; }
.v{ color: var(--muted); font-size: 14px; line-height: 1.65; }

/* Inline code */
code, .code{
  font-family: var(--mono);
  background: rgba(15,23,42,0.05);
  border: 1px solid rgba(15,23,42,0.10);
  padding: 2px 6px;
  border-radius: 8px;
  color: #0f172a;
}

/* Footer */
.footer{
  margin-top: 22px;
  color: var(--muted2);
  font-size: 12px;
  text-align: center;
}

/* Textareas / code blocks */
textarea, pre{
  border-radius: 14px;
  border: 1px solid rgba(15,23,42,0.12);
  background: rgba(255,255,255,0.95);
  color: #0f172a;
  font-family: var(--mono);
}

/* ===== Flat layout overrides ===== */
.hero{
  border: 0;
  background: transparent;
  box-shadow: none;
  padding: 0;
}
.hero:before{ display:none; }
.hero p{ max-width: 95ch; }

.grid2 > section{
  border: 0;
  background: transparent;
  box-shadow: none;
  padding: 0;
}
.grid2 h2{
  margin-top: 0;
}

.figure{
  border: 0;
  background: transparent;
  box-shadow: none;
  border-radius: 0;
}
.figcap{
  border-top: 0;
  padding-left: 0;
  padding-right: 0;
}

/* ===== Single-column (no left/right) ===== */
.grid2{
  display: block;          /* grid 해제 */
  margin-top: 18px;
}

.grid2 > *{
  width: 100%;
  margin-top: 18px;        /* 섹션 사이 간격 */
}

.grid2 > *:first-child{
  margin-top: 0;
}

/* TOC도 두 칼럼이면 한 칼럼으로 */
.toc{
  grid-template-columns: 1fr;
}

.figure img{
  width: min(520px, 100%);
  height: auto;
  display: block;
  margin: 0 auto;
}

/* ===== Auto-card every section except .hero ===== */
.wrap > section:not(.hero){
  border: 1px solid var(--border);
  background: var(--card);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 18px;
  margin-top: 18px;
}

:root{
  /* Rubik’s cube colors */
  --cube-red:    #e53935;
  --cube-orange: #fb8c00;
  --cube-yellow: #fdd835;
  --cube-green:  #43a047;
  --cube-blue:   #1e88e5;
  --cube-white:  #f5f7ff;
}

/* ===== TOC bottom color underline (Rubik’s colors) ===== */
.toc a{
  position: relative; /* needed for pseudo-element */
  overflow: hidden;   /* keep underline corners clean */
}

/* optional: hover glow (still no layout change) */
.toc a:hover::after{
  filter: drop-shadow(0 6px 10px rgba(2,6,23,0.18));
}

/* ===== Header LED strip ===== */
:root{
  --cube-rainbow: linear-gradient(90deg,
    var(--cube-red), var(--cube-orange), var(--cube-yellow),
    var(--cube-green), var(--cube-blue), #8e24aa, var(--cube-red)
  );
}

.header{
  position: sticky;
}

/* optional: subtle moving light */
@media (prefers-reduced-motion: no-preference){
  .header::after{
    background-size: 200% 100%;
    animation: ledMove 6s linear infinite;
  }
  @keyframes ledMove{
    0%{ background-position: 0% 50%; }
    100%{ background-position: 200% 50%; }
  }
}

/* ===== TOC premium hover ===== */
.toc a{
  transition: transform .12s ease, box-shadow .20s ease, border-color .20s ease;
  will-change: transform;
}

.toc a:hover{
  transform: translateY(-2px);
  box-shadow: 0 14px 30px rgba(2,6,23,0.10);
  border-color: rgba(15,23,42,0.16);
}

/* ===== Tag chips with cube tint ===== */
.tag{
  position: relative;
  padding-left: 12px;
}

.tag::before{
  content:"";
  width: 10px; height: 10px;
  border-radius: 3px;
  display: inline-block;
  margin-right: 8px;
  background: var(--cube-blue);
  box-shadow: 0 6px 14px rgba(2,6,23,0.10);
  vertical-align: -1px;
}

/* cycle tag colors */
.metaRow .tag:nth-child(6n+1)::before{ background: var(--cube-red); }
.metaRow .tag:nth-child(6n+2)::before{ background: var(--cube-yellow); }
.metaRow .tag:nth-child(6n+3)::before{ background: var(--cube-blue); }
.metaRow .tag:nth-child(6n+4)::before{ background: var(--cube-green); }
.metaRow .tag:nth-child(6n+5)::before{ background: var(--cube-orange); }
.metaRow .tag:nth-child(6n)::before  { background: var(--cube-white); }

/* ===== H1: subtle Rubik rainbow gradient text ===== */
:root{
  --cube-rainbow: linear-gradient(90deg,
    var(--cube-red),
    var(--cube-orange),
    var(--cube-yellow),
    var(--cube-green),
    var(--cube-blue),
    #8e24aa,
    var(--cube-red)
  );
}

/* fallback if background-clip not supported */
@supports not ((-webkit-background-clip: text) or (background-clip: text)){
  .hero h1{ color: var(--text); }
}

:root{
  --headerH: 100px; /* 顶栏高度：不对就调大/调小 */
}

/* 让顶部标题栏永远固定 */
.header{
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 1000;

  /* 你的原样式里有负 margin，fixed 时要去掉 */
  margin: 0;
  padding: 12px 18px;

  backdrop-filter: blur(10px);
  background: rgba(246,247,251,0.80);
  border-bottom: 1px solid var(--border);
}

/* 给正文留出空间，避免被 fixed 顶栏遮住 */
.wrap{
  padding-top: calc(22px + var(--headerH));
}

/* 可选：点击目录/锚点时不被顶栏盖住 */
html{ scroll-padding-top: var(--headerH); }

body{
  margin: 0;
  font-family: var(--sans);
  color: var(--text);
  background:
    radial-gradient(900px 520px at 15% 10%, rgba(168,85,247,0.18), transparent 60%),
    radial-gradient(900px 520px at 85% 20%, rgba(30,136,229,0.18), transparent 60%),
    radial-gradient(900px 520px at 40% 110%, rgba(67,160,71,0.16), transparent 60%),
    conic-gradient(from 220deg at 60% 40%,
      rgba(229,57,53,0.08),
      rgba(253,216,53,0.08),
      rgba(30,136,229,0.08),
      rgba(67,160,71,0.08),
      rgba(251,140,0,0.08),
      rgba(229,57,53,0.08)
    ),
    linear-gradient(180deg, #f7f8fc, #eef2f7);
}

.hero h1{
  -webkit-text-stroke: 1px rgba(15,23,42,0.35); /* 轮廓线 */
}