/* =========================================================================
   HOPE — Nested Learning, explained.
   A reading-first, editorial layout with a multi-frequency oscillation motif.
   ========================================================================= */

:root {
  /* Light "manuscript" palette */
  --paper:        #f4f0e6;
  --paper-2:      #ece6d8;
  --card:         #fbf8f0;
  --ink:          #211d18;
  --ink-soft:     #4a4339;
  --ink-faint:    #837a6c;
  --rule:         #d8cfba;
  --rule-soft:    #e4ddcb;
  --accent:       #b4541e;   /* burnt amber — synaptic */
  --accent-2:     #1f6f6b;   /* deep teal — secondary frequency */
  --accent-3:     #8a6d1f;   /* ochre — third band */
  --code-bg:      #2a2620;
  --code-ink:     #ece4d2;
  --mark:         rgba(180, 84, 30, 0.14);
  --shadow:       0 1px 2px rgba(33,29,24,.06), 0 8px 30px rgba(33,29,24,.07);

  --serif: "Newsreader", "Iowan Old Style", "Palatino Linotype", "Source Serif 4", Georgia, "Times New Roman", serif;
  --sans:  "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", "Pretendard", "Apple SD Gothic Neo", "Noto Sans KR", sans-serif;
  --mono:  "JetBrains Mono", "SF Mono", "Fira Code", ui-monospace, Menlo, Consolas, monospace;

  --measure: 44rem;
}

html[data-theme="dark"] {
  --paper:        #16140f;
  --paper-2:      #1d1a14;
  --card:         #1f1c15;
  --ink:          #ece4d2;
  --ink-soft:     #c4bba8;
  --ink-faint:    #8f8772;
  --rule:         #34301f;
  --rule-soft:    #2a2619;
  --accent:       #e08a4e;
  --accent-2:     #5fb8b1;
  --accent-3:     #d4ad4e;
  --code-bg:      #100e0a;
  --code-ink:     #ddd4c0;
  --mark:         rgba(224, 138, 78, 0.18);
  --shadow:       0 1px 2px rgba(0,0,0,.3), 0 10px 40px rgba(0,0,0,.4);
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: 5.2rem; -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--serif);
  font-size: 1.18rem;
  line-height: 1.72;
  font-feature-settings: "kern" 1, "liga" 1, "onum" 1;
  -webkit-font-smoothing: antialiased;
  transition: background .4s ease, color .4s ease;
}

::selection { background: var(--mark); }

/* --------------------------------------------------------------- top bar */
.topbar {
  position: fixed; inset: 0 0 auto 0; z-index: 50;
  display: flex; align-items: center; gap: 1rem;
  height: 4rem; padding: 0 clamp(1rem, 4vw, 2.5rem);
  background: color-mix(in srgb, var(--paper) 86%, transparent);
  backdrop-filter: saturate(150%) blur(12px);
  -webkit-backdrop-filter: saturate(150%) blur(12px);
  border-bottom: 1px solid var(--rule);
  font-family: var(--sans);
}
.topbar .brand {
  display: flex; align-items: center; gap: .6rem;
  font-weight: 700; letter-spacing: -0.01em; font-size: 1.02rem;
  color: var(--ink); text-decoration: none;
}
.topbar .brand .dot {
  width: .85rem; height: .85rem; border-radius: 50%;
  background: radial-gradient(circle at 30% 30%, var(--accent), var(--accent-3));
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--accent) 22%, transparent);
}
.topbar .brand small { color: var(--ink-faint); font-weight: 500; }
.topbar .spacer { flex: 1; }

.toolbtn, .langtoggle button {
  font-family: var(--sans); font-size: .82rem; font-weight: 600;
  color: var(--ink-soft); background: transparent;
  border: 1px solid var(--rule); border-radius: 999px;
  padding: .42rem .8rem; cursor: pointer; line-height: 1;
  transition: all .18s ease;
}
.toolbtn:hover { border-color: var(--accent); color: var(--accent); }
.langtoggle { display: inline-flex; border: 1px solid var(--rule); border-radius: 999px; overflow: hidden; }
.langtoggle button { border: none; border-radius: 0; padding: .42rem .85rem; }
.langtoggle button.active { background: var(--accent); color: #fff; }
.topbar a.gh { color: var(--ink-soft); display: inline-flex; }
.topbar a.gh:hover { color: var(--accent); }

/* reading progress */
#progress {
  position: fixed; top: 4rem; left: 0; height: 2px; width: 0;
  background: linear-gradient(90deg, var(--accent), var(--accent-3), var(--accent-2));
  z-index: 51; transition: width .1s linear;
}

/* --------------------------------------------------------------- layout */
.shell { display: grid; grid-template-columns: 1fr; }
@media (min-width: 1080px) {
  .shell { grid-template-columns: minmax(0,1fr) 17rem; }
  .shell .toc-rail { grid-column: 2; }
}

main { max-width: 100%; }

.wrap { width: min(var(--measure), calc(100% - 2.5rem)); margin: 0 auto; }

/* --------------------------------------------------------------- hero */
.hero { position: relative; padding-top: 4rem; overflow: hidden; border-bottom: 1px solid var(--rule); }
.hero canvas { position: absolute; inset: 0; width: 100%; height: 100%; opacity: .55; }
.hero .hero-inner { position: relative; padding: clamp(3.5rem, 9vw, 7rem) 0 clamp(3rem,7vw,5rem); }
.hero .eyebrow {
  font-family: var(--sans); font-weight: 600; font-size: .8rem; letter-spacing: .16em;
  text-transform: uppercase; color: var(--accent); margin: 0 0 1.1rem;
}
.hero h1 {
  font-size: clamp(2.6rem, 7vw, 4.6rem); line-height: 1.02; margin: 0 0 1.3rem;
  letter-spacing: -0.02em; font-weight: 600;
}
.hero h1 .il { font-style: italic; color: var(--accent); }
.hero .lede { font-size: clamp(1.2rem, 2.4vw, 1.5rem); color: var(--ink-soft); margin: 0 0 2rem; max-width: 36rem; }
.hero .meta { font-family: var(--sans); font-size: .9rem; color: var(--ink-faint); display: flex; flex-wrap: wrap; gap: .4rem 1.4rem; }
.hero .meta a { color: var(--accent-2); text-decoration: none; border-bottom: 1px solid color-mix(in srgb, var(--accent-2) 35%, transparent); }
.hero .cta { margin-top: 2.4rem; display: flex; gap: .8rem; flex-wrap: wrap; font-family: var(--sans); }
.cta a {
  text-decoration: none; font-weight: 600; font-size: .95rem; padding: .7rem 1.3rem;
  border-radius: 999px; transition: transform .15s ease, box-shadow .15s ease;
}
.cta a.primary { background: var(--accent); color: #fff; box-shadow: var(--shadow); }
.cta a.primary:hover { transform: translateY(-2px); }
.cta a.ghost { color: var(--ink); border: 1px solid var(--rule); }
.cta a.ghost:hover { border-color: var(--accent); color: var(--accent); }

/* --------------------------------------------------------------- prose */
article { padding: clamp(2.5rem, 6vw, 4.5rem) 0; }

section.chapter { scroll-margin-top: 5rem; }
section.chapter + section.chapter { margin-top: clamp(2.5rem, 6vw, 4.5rem); }

.chapter-no {
  font-family: var(--sans); font-size: .8rem; font-weight: 700; letter-spacing: .15em;
  text-transform: uppercase; color: var(--accent); margin-bottom: .5rem;
}
h2 {
  font-size: clamp(1.9rem, 4.2vw, 2.7rem); line-height: 1.12; letter-spacing: -0.018em;
  font-weight: 600; margin: 0 0 1.3rem;
}
h3 {
  font-size: clamp(1.35rem, 3vw, 1.7rem); line-height: 1.2; letter-spacing: -0.01em;
  font-weight: 600; margin: 2.6rem 0 .9rem;
}
h4 { font-family: var(--sans); font-size: 1rem; font-weight: 700; margin: 2rem 0 .6rem; color: var(--ink); letter-spacing: -0.005em; }

p { margin: 0 0 1.3rem; }
.prose p:first-of-type.dropcap::first-letter,
p.dropcap::first-letter {
  initial-letter: 3 3;
  -webkit-initial-letter: 3 3;
  font-weight: 600; color: var(--accent); margin-right: .6rem;
}
a.inline { color: var(--accent-2); text-decoration: none; border-bottom: 1px solid color-mix(in srgb, var(--accent-2) 35%, transparent); }
a.inline:hover { border-color: var(--accent-2); }

strong { font-weight: 700; color: var(--ink); }
em { font-style: italic; }
mark { background: var(--mark); color: inherit; padding: 0 .15em; border-radius: 2px; }

ul, ol { margin: 0 0 1.4rem; padding-left: 1.4rem; }
li { margin: 0 0 .55rem; }
li::marker { color: var(--accent); }

blockquote {
  margin: 1.8rem 0; padding: .2rem 0 .2rem 1.5rem;
  border-left: 3px solid var(--accent);
  color: var(--ink-soft); font-style: italic; font-size: 1.12rem;
}
blockquote cite { display: block; font-style: normal; font-family: var(--sans); font-size: .82rem; color: var(--ink-faint); margin-top: .6rem; }

hr.sep { border: none; text-align: center; margin: 3rem 0; color: var(--ink-faint); }
hr.sep::before { content: "·  ·  ·"; letter-spacing: .6em; }

/* lead paragraph after a heading */
.lead { font-size: 1.28rem; color: var(--ink-soft); }

/* --------------------------------------------------------------- callouts */
.callout {
  margin: 1.8rem 0; padding: 1.2rem 1.4rem; border-radius: 14px;
  background: var(--card); border: 1px solid var(--rule); box-shadow: var(--shadow);
  font-size: 1.02rem;
}
.callout .tag {
  font-family: var(--sans); font-size: .72rem; font-weight: 700; letter-spacing: .12em;
  text-transform: uppercase; display: inline-block; margin-bottom: .5rem;
  padding: .2rem .6rem; border-radius: 999px;
}
.callout p:last-child { margin-bottom: 0; }
.callout.code-map { border-left: 4px solid var(--accent-2); }
.callout.code-map .tag { color: var(--accent-2); background: color-mix(in srgb, var(--accent-2) 14%, transparent); }
.callout.intuition { border-left: 4px solid var(--accent); }
.callout.intuition .tag { color: var(--accent); background: color-mix(in srgb, var(--accent) 14%, transparent); }
.callout.warn { border-left: 4px solid var(--accent-3); }
.callout.warn .tag { color: var(--accent-3); background: color-mix(in srgb, var(--accent-3) 16%, transparent); }
.callout code { font-family: var(--mono); font-size: .9em; background: color-mix(in srgb, var(--ink) 8%, transparent); padding: .08em .35em; border-radius: 4px; }

/* --------------------------------------------------------------- code */
pre {
  margin: 1.6rem 0; padding: 1.2rem 1.3rem; border-radius: 14px;
  background: var(--code-bg); color: var(--code-ink);
  overflow-x: auto; font-family: var(--mono); font-size: .86rem; line-height: 1.62;
  box-shadow: var(--shadow); border: 1px solid color-mix(in srgb, #000 25%, var(--code-bg));
  -webkit-overflow-scrolling: touch;
}
pre code { font-family: var(--mono); background: none; padding: 0; }
:not(pre) > code {
  font-family: var(--mono); font-size: .86em;
  background: color-mix(in srgb, var(--ink) 9%, transparent);
  padding: .1em .38em; border-radius: 5px; color: var(--ink);
}
.codecap {
  font-family: var(--sans); font-size: .78rem; color: var(--ink-faint);
  margin: -1rem 0 1.8rem; padding-left: .2rem;
}
.codecap b { color: var(--accent-2); font-weight: 600; }

/* --------------------------------------------------------------- math */
.katex-display { margin: 1.6rem 0; overflow-x: auto; overflow-y: hidden; padding: .4rem 0; }
.eqbox {
  margin: 1.7rem 0; padding: 1rem 1.2rem; border-radius: 12px;
  background: var(--paper-2); border: 1px solid var(--rule-soft);
  position: relative;
}
.eqbox .eqno { position: absolute; right: 1rem; top: 50%; transform: translateY(-50%); font-family: var(--sans); font-size: .75rem; color: var(--ink-faint); }
.eqbox .katex-display { margin: 0; }

/* --------------------------------------------------------------- figures */
figure { margin: 2rem 0; }
figure img {
  width: 100%; height: auto; border-radius: 14px;
  border: 1px solid var(--rule); box-shadow: var(--shadow); background: var(--card);
}
figure.bench img { background: #fff; padding: .4rem; }
figcaption { font-family: var(--sans); font-size: .82rem; color: var(--ink-faint); margin-top: .7rem; text-align: center; }
figcaption b { color: var(--ink-soft); }

/* diagram (pure CSS pipeline) */
.pipeline {
  display: flex; flex-wrap: wrap; align-items: stretch; gap: .55rem;
  margin: 2rem 0; font-family: var(--sans);
}
.pipeline .stage {
  flex: 1 1 8rem; min-width: 7rem; padding: .9rem .8rem; border-radius: 12px;
  background: var(--card); border: 1px solid var(--rule); text-align: center;
  display: flex; flex-direction: column; justify-content: center; box-shadow: var(--shadow);
}
.pipeline .stage .s-t { font-weight: 700; font-size: .9rem; }
.pipeline .stage .s-d { font-size: .74rem; color: var(--ink-faint); margin-top: .25rem; }
.pipeline .stage.sm { border-top: 3px solid var(--accent); }
.pipeline .stage.cms { border-top: 3px solid var(--accent-2); }
.pipeline .stage.attn { border-top: 3px solid var(--accent-3); }
.pipeline .stage.head { border-top: 3px solid var(--ink-faint); }
.pipeline .arr { display: flex; align-items: center; color: var(--ink-faint); font-size: 1.1rem; }
@media (max-width: 620px){ .pipeline { flex-direction: column; } .pipeline .arr { transform: rotate(90deg); justify-content: center; } }

/* frequency band table */
.bands { margin: 2rem 0; display: grid; gap: .6rem; }
.band {
  display: grid; grid-template-columns: 7rem 1fr; gap: 1rem; align-items: center;
  padding: .8rem 1rem; border-radius: 12px; background: var(--card); border: 1px solid var(--rule);
}
.band .wave { height: 2.4rem; }
.band .lbl { font-family: var(--sans); }
.band .lbl b { display:block; }
.band .lbl span { font-size: .8rem; color: var(--ink-faint); }

/* --------------------------------------------------------------- TOC rail */
.toc-rail { display: none; }
@media (min-width: 1080px) {
  .toc-rail { display: block; }
  .toc-sticky {
    position: sticky; top: 5.4rem; padding: 0 1.5rem 2rem 0;
    font-family: var(--sans); font-size: .82rem; max-height: calc(100vh - 6rem); overflow-y: auto;
  }
  .toc-sticky .toc-h { font-size: .72rem; letter-spacing: .14em; text-transform: uppercase; color: var(--ink-faint); margin-bottom: .8rem; font-weight: 700; }
  .toc-sticky a {
    display: block; color: var(--ink-faint); text-decoration: none; padding: .28rem 0 .28rem .8rem;
    border-left: 2px solid var(--rule); line-height: 1.35; transition: all .15s ease;
  }
  .toc-sticky a:hover { color: var(--ink); }
  .toc-sticky a.active { color: var(--accent); border-left-color: var(--accent); font-weight: 600; }
  .toc-sticky a .tnum { color: var(--accent); font-weight: 700; margin-right: .4rem; }
}

/* --------------------------------------------------------------- footer */
footer {
  border-top: 1px solid var(--rule); margin-top: 4rem;
  padding: 3rem 0; font-family: var(--sans); font-size: .9rem; color: var(--ink-faint);
}
footer .wrap { display: flex; flex-wrap: wrap; gap: 1.5rem; justify-content: space-between; }
footer a { color: var(--accent-2); text-decoration: none; }
footer a:hover { text-decoration: underline; }
footer .cite { font-family: var(--mono); font-size: .78rem; background: var(--code-bg); color: var(--code-ink); padding: 1rem 1.2rem; border-radius: 12px; width: 100%; white-space: pre-wrap; line-height: 1.6; margin-top: 1rem; }

/* overview — editorial label/value rows */
.brief { margin: 2.4rem 0 1rem; border-top: 1px solid var(--rule); }
.brief-row {
  display: grid; grid-template-columns: 1fr; gap: .4rem;
  padding: 1.5rem 0; border-bottom: 1px solid var(--rule);
}
@media (min-width: 720px){ .brief-row { grid-template-columns: 9.5rem 1fr; gap: 2.2rem; } }
.brief-k {
  font-family: var(--sans); font-weight: 700; font-size: .78rem;
  letter-spacing: .13em; text-transform: uppercase; color: var(--accent); padding-top: .35rem;
}
.brief-k span { display: block; font-family: var(--serif); font-weight: 500; font-size: 1.05rem;
  letter-spacing: 0; text-transform: none; color: var(--ink-faint); margin-top: .25rem; }
.brief-v { font-size: 1.08rem; line-height: 1.66; }
.brief-v p { margin: 0; color: var(--ink-soft); }
.brief-v ul { margin: 0; padding-left: 1.1rem; }
.brief-v li { margin-bottom: .5rem; }
.brief-v li:last-child { margin-bottom: 0; }

/* lang visibility */
[data-lang-block] { display: none; }
html[data-lang="ko"] [data-lang-block="ko"] { display: revert; }
html[data-lang="en"] [data-lang-block="en"] { display: revert; }
/* inline spans */
html[data-lang="ko"] [data-lang="en"].swap { display: none; }
html[data-lang="en"] [data-lang="ko"].swap { display: none; }

/* keep TOC text swap inline */
.toc-sticky [data-lang-block] { }

/* fade-in on scroll */
.reveal { opacity: 0; transform: translateY(14px); transition: opacity .6s ease, transform .6s ease; }
.reveal.in { opacity: 1; transform: none; }
@media (prefers-reduced-motion: reduce) { .reveal { opacity:1; transform:none; transition:none; } html{scroll-behavior:auto;} }

/* small screens topbar trim */
@media (max-width: 680px) {
  .topbar .brand small { display: none; }
  .toolbtn.wide { display: none; }
}