/* Crypto-IT – the only stylesheet.
   1. Variables (light / dark)   2. Base   3. Header   4. Layout + sidebar
   5. Article   6. Cards (section pages)   7. Tools   8. Footer   */

/* ---------- 1. Variables ---------- */
:root {
  color-scheme: light dark;
  --bg: #fbfbfd;
  --surface: #ffffff;
  --text: #1c2230;
  --muted: #5b6475;
  --border: #e2e5ec;
  --accent: #3b50c9;
  --accent-soft: #eef0fc;
  --code-bg: #f3f4f8;
  --header-bg: #11182b;
  --header-text: #e8ebf5;
  --radius: 10px;
  --font: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --mono: ui-monospace, "Cascadia Code", "SFMono-Regular", Menlo, Consolas, monospace;
  --content: 46rem;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0f1422;
    --surface: #161c2d;
    --text: #e3e7f1;
    --muted: #9aa3b8;
    --border: #2a3248;
    --accent: #93a4ff;
    --accent-soft: #1e2645;
    --code-bg: #1b2236;
    --header-bg: #0a0e19;
  }
}

/* ---------- 2. Base ---------- */
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-padding-top: 1rem; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 1.0625rem/1.65 var(--font);
}
img { max-width: 100%; height: auto; }
a { color: var(--accent); text-underline-offset: 0.15em; }
a:hover { text-decoration-thickness: 2px; }
:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }
h1, h2, h3 { line-height: 1.25; }
code, kbd, samp { font-family: var(--mono); font-size: 0.92em; }

.skip-link { position: absolute; left: -999px; }
.skip-link:focus { left: 1rem; top: 1rem; z-index: 10; padding: 0.5rem 1rem; background: var(--surface); }

.visually-hidden {
  position: absolute; width: 1px; height: 1px; overflow: hidden;
  clip: rect(0 0 0 0); white-space: nowrap;
}

/* ---------- 3. Header ---------- */
.site-header { background: var(--header-bg); color: var(--header-text); }
.site-header__inner {
  display: flex;
  align-items: center;
  gap: 1rem 2rem;
  max-width: 76rem;
  margin: 0 auto;
  padding: 0.75rem 1.25rem;
  flex-wrap: wrap;
}
.logo {
  color: inherit;
  font: 700 1.35rem/1 var(--mono);
  letter-spacing: -0.02em;
  text-decoration: none;
}
.logo span { color: #93a4ff; }
.site-nav { flex: 1; min-width: 0; }
.site-nav ul {
  display: flex;
  gap: 0.25rem;
  margin: 0;
  padding: 0;
  list-style: none;
  overflow-x: auto;           /* narrow screens: menu scrolls sideways */
  scrollbar-width: none;
}
.site-nav a, .lang-switch {
  display: block;
  padding: 0.4rem 0.7rem;
  border-radius: 6px;
  color: var(--header-text);
  font-size: 0.95rem;
  text-decoration: none;
  white-space: nowrap;
}
.site-nav a:hover, .lang-switch:hover { background: #ffffff1a; }
.site-nav a[aria-current] { background: #ffffff26; }
.lang-switch { border: 1px solid #ffffff40; font-weight: 600; }

@media (max-width: 720px) {
  .site-nav { order: 3; flex-basis: 100%; }
  .lang-switch { margin-left: auto; }
}

/* ---------- 4. Layout + sidebar ---------- */
.layout {
  display: grid;
  grid-template-columns: 15rem minmax(0, var(--content));
  gap: 3rem;
  justify-content: center;
  max-width: 76rem;
  margin: 0 auto;
  padding: 2rem 1.25rem 3rem;
}
.layout > main { grid-column: 2; grid-row: 1; }
.layout > .sidebar { grid-column: 1; grid-row: 1; }
.layout--wide { grid-template-columns: minmax(0, 68rem); }
.layout--wide > main { grid-column: 1; }

@media (max-width: 960px) {
  .layout { grid-template-columns: minmax(0, var(--content)); gap: 2rem; }
  .layout > main, .layout > .sidebar { grid-column: 1; grid-row: auto; }
}

.sidebar { font-size: 0.93rem; }
.sidebar__inner { position: sticky; top: 1rem; max-height: calc(100vh - 2rem); overflow-y: auto; }
.sidebar h2 { margin: 0 0 0.5rem; font-size: 0.8rem; letter-spacing: 0.08em; text-transform: uppercase; color: var(--muted); }
.sidebar ul { margin: 0; padding: 0; list-style: none; }
.sidebar ul ul { margin: 0.1rem 0 0.4rem 0.75rem; padding-left: 0.6rem; border-left: 1px solid var(--border); }
.sidebar a { display: block; padding: 0.15rem 0; color: var(--text); text-decoration: none; }
.sidebar a:hover { color: var(--accent); }
.sidebar a[aria-current] { color: var(--accent); font-weight: 600; }

/* ---------- 5. Article ---------- */
.breadcrumbs ol { display: flex; flex-wrap: wrap; gap: 0.25rem; margin: 0 0 1rem; padding: 0; list-style: none; font-size: 0.9rem; color: var(--muted); }
.breadcrumbs li + li::before { content: "›"; margin-right: 0.25rem; }
.breadcrumbs a { color: var(--muted); }

.article__title { margin: 0; font-size: clamp(2rem, 4vw, 2.6rem); letter-spacing: -0.02em; }
.article__subtitle { margin: 0.25rem 0 0; color: var(--muted); font-size: 1.15rem; }
.article__meta { margin: 0.75rem 0 1.5rem; color: var(--muted); font-size: 0.9rem; }
.article__lead { font-size: 1.15rem; }
.article__body h2 { margin: 2.25rem 0 0.75rem; font-size: 1.55rem; }
.article__body h3 { margin: 1.75rem 0 0.5rem; font-size: 1.2rem; }
.article__body li { margin-bottom: 0.3rem; }

.toc {
  margin: 1.5rem 0;
  padding: 1rem 1.25rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  font-size: 0.95rem;
}
.toc h2 { margin: 0 0 0.25rem; font-size: 0.8rem; letter-spacing: 0.08em; text-transform: uppercase; color: var(--muted); }
.toc ol { margin: 0; padding-left: 1.25rem; }

.term { font-family: var(--mono); font-size: 0.95em; padding: 0 0.2em; border-radius: 4px; background: var(--code-bg); }

pre {
  position: relative;
  margin: 1.25rem 0;
  padding: 1rem 1.25rem;
  overflow-x: auto;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--code-bg);
  font-size: 0.88rem;
  line-height: 1.55;
}
.code-copy {
  position: absolute;
  top: 0.5rem;
  right: 0.5rem;
  padding: 0.2rem 0.6rem;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--surface);
  color: var(--muted);
  font: 0.8rem var(--font);
  cursor: pointer;
}

.matrix { border-collapse: collapse; margin: 1rem 0; font: 600 1.05rem var(--mono); text-transform: uppercase; }
.matrix td { width: 2.4em; height: 2.4em; border: 1px solid var(--border); background: var(--surface); text-align: center; }

.pager { display: grid; grid-template-columns: 1fr 1fr; gap: 1rem; margin-top: 3rem; }
.pager a {
  display: block;
  padding: 0.9rem 1.1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  text-decoration: none;
}
.pager a:hover { border-color: var(--accent); }
.pager small { display: block; color: var(--muted); }
.pager__next { grid-column: 2; text-align: right; }

.share { margin-top: 2rem; font-size: 0.9rem; color: var(--muted); }
.share a { margin-left: 0.5rem; }

/* Content elements (converted articles) */
.math { font-family: Georgia, "Times New Roman", serif; font-style: italic; overflow-wrap: anywhere; }
var { font-family: Georgia, "Times New Roman", serif; }
.steps li::marker { font-weight: 700; color: var(--accent); }

.figure { margin: 1.5rem 0; text-align: center; }
.figure img { display: inline-block; border-radius: 6px; background: #fff; }   /* diagrams have transparent/white backgrounds */
.figure figcaption, .caption { margin-top: 0.4rem; color: var(--muted); font-size: 0.9rem; text-align: center; }
.figure--right { float: right; max-width: 45%; margin: 0 0 1rem 1.5rem; }
@media (max-width: 600px) { .figure--right { float: none; max-width: 100%; margin: 1.5rem 0; } }

.table-wrap { margin: 1.25rem 0; overflow-x: auto; }
.table { border-collapse: collapse; font-size: 0.95rem; }
.table th, .table td { padding: 0.35rem 0.6rem; border: 1px solid var(--border); text-align: left; vertical-align: top; }
.table th { background: var(--code-bg); font-weight: 600; }
.table caption { caption-side: bottom; padding-top: 0.4rem; color: var(--muted); font-size: 0.9rem; }
.table--matrix th, .table--matrix td { text-align: center; font-family: var(--mono); }
.table--plain th, .table--plain td { border-color: transparent; }

/* inline matrix equations: <div class="equation"><span>K =</span><table class="eq-matrix">…</table></div> */
.equation { display: flex; flex-wrap: wrap; align-items: center; gap: 0.5rem 0.6rem; margin: 1rem 0; font-family: var(--mono); font-size: 0.95rem; overflow-x: auto; }
.eq-matrix { border-collapse: separate; border-spacing: 0; border-left: 2px solid var(--text); border-right: 2px solid var(--text); border-radius: 6px; }
.eq-matrix td { padding: 0.15rem 0.6rem; border: 0; text-align: center; white-space: nowrap; }
.table--bold { border: 2px solid var(--text); }
.table--big { font-size: 1.05rem; }
.table .row-border > *, .table .cell-border { border-bottom: 2px solid var(--text); }
.row-vertical th { vertical-align: bottom; }
.vertical { display: inline-block; writing-mode: vertical-rl; transform: rotate(180deg); }

.definition { margin: 1.5rem 0; padding: 1rem 1.25rem; border-left: 4px solid var(--accent); border-radius: 0 var(--radius) var(--radius) 0; background: var(--accent-soft); }
.definition__title { margin: 0 0 0.25rem; font-weight: 700; color: var(--accent); }
.definition__note { margin-top: 0.75rem; font-size: 0.95rem; }

/* Side notes: a term in the text opens a small panel (native popover, no JavaScript) */
.note-ref {
  padding: 0;
  border: 0;
  border-bottom: 1px dashed var(--accent);
  background: none;
  color: var(--accent);
  font: inherit;
  cursor: help;
}
.note {
  max-width: min(32rem, calc(100vw - 2rem));
  margin: auto;
  padding: 1.25rem 1.5rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--text);
  box-shadow: 0 10px 40px #00000040;
}
.note::backdrop { background: #0000004d; }
.note__close { float: right; margin: 0.5rem 0 0; padding: 0.3rem 0.8rem; border: 1px solid var(--border); border-radius: 6px; background: var(--bg); color: var(--text); font: inherit; cursor: pointer; }

.section-index ul { padding-left: 1.2rem; }
.section-index > ul { columns: 2 18rem; column-gap: 2rem; }
.section-index li { break-inside: avoid; margin: 0.15rem 0; }
.section-index li > ul { margin: 0.15rem 0 0.4rem; }

.sidebar h2 a { color: inherit; text-decoration: none; }

/* ---------- 6. Cards (section pages) ---------- */
.cards { display: grid; grid-template-columns: repeat(auto-fill, minmax(15rem, 1fr)); gap: 1.25rem; margin: 2rem 0; padding: 0; list-style: none; }
.card {
  position: relative;
  display: flex;
  flex-direction: column;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  overflow: hidden;
}
.card:hover { border-color: var(--accent); }
.card img { display: block; width: 100%; aspect-ratio: 16 / 10; object-fit: contain; background: var(--accent-soft); }
.card__body { padding: 1rem 1.1rem 1.2rem; }
.card h2, .card h3 { margin: 0 0 0.4rem; font-size: 1.15rem; }
.card a { text-decoration: none; }
.card a::after { content: ""; position: absolute; inset: 0; }   /* whole card clickable */
.card p { margin: 0; color: var(--muted); font-size: 0.95rem; }
.badge { display: inline-block; margin-left: 0.35rem; padding: 0.05rem 0.45rem; border-radius: 99px; background: var(--accent-soft); color: var(--accent); font-size: 0.72rem; font-weight: 600; vertical-align: middle; }

.link-list { columns: 2 16rem; padding-left: 1.2rem; }

/* ---------- 7. Tools ---------- */
.tool {
  margin: 2rem 0;
  padding: 1.25rem 1.5rem 1.5rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  box-shadow: 0 1px 3px #0000000d;
}
.tool > h2 { margin-top: 0; }
.tool__grid { display: grid; grid-template-columns: minmax(0, 1fr) auto; gap: 1rem 1.5rem; align-items: start; }
@media (max-width: 600px) { .tool__grid { grid-template-columns: minmax(0, 1fr); } }
.field { display: grid; gap: 0.3rem; margin-bottom: 1rem; }
.field label, .tool legend { font-weight: 600; font-size: 0.95rem; }
.field small { color: var(--muted); font-size: 0.85rem; }
.tool input[type="text"], .tool textarea {
  width: 100%;
  padding: 0.55rem 0.7rem;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--bg);
  color: var(--text);
  font: 1rem var(--mono);
}
.tool textarea { min-height: 6rem; resize: vertical; }
.tool textarea[readonly] { background: var(--code-bg); }
.tool fieldset { margin: 0 0 1rem; padding: 0; border: 0; }
.options { display: flex; flex-wrap: wrap; gap: 0.25rem 1rem; }
.options label { display: inline-flex; gap: 0.35rem; align-items: center; font-size: 0.95rem; }
.segmented { display: inline-flex; border: 1px solid var(--border); border-radius: 8px; overflow: hidden; }
.segmented label { padding: 0.4rem 0.9rem; cursor: pointer; }
.segmented input { position: absolute; opacity: 0; }
.segmented label:has(input:checked) { background: var(--accent); color: var(--surface); }
.segmented label:has(input:focus-visible) { outline: 3px solid var(--accent); outline-offset: -3px; }
.tool__actions { display: flex; gap: 0.5rem; margin-top: 0.5rem; }
.button {
  padding: 0.45rem 1rem;
  border: 1px solid var(--accent);
  border-radius: 6px;
  background: transparent;
  color: var(--accent);
  font: 600 0.95rem var(--font);
  cursor: pointer;
}
.button:hover { background: var(--accent-soft); }
.tool__steps { font: 0.95rem var(--mono); color: var(--muted); word-break: break-word; }
.tool__error { color: #c62828; font-weight: 600; }
@media (prefers-color-scheme: dark) { .tool__error { color: #ff8a80; } }
.tool .matrix { margin: 0; }
.tool figure { max-width: 100%; margin: 0; overflow-x: auto; }
/* Two- and four-square widgets show more than one key table next to the controls. */
.matrix-pair, .matrix-quad { margin: 0; padding: 0; }
.matrix-pair { display: flex; flex-wrap: wrap; gap: 0.75rem; }
.matrix-quad { display: grid; grid-template-columns: auto auto; gap: 0.4rem; width: max-content; }
.matrix-pair .matrix, .matrix-quad .matrix { font-size: 0.9rem; }
.matrix-pair .matrix td, .matrix-quad .matrix td { width: 1.9em; height: 1.9em; }

/* Homepage */
.hero { margin: 1rem 0 2.5rem; padding: 2.5rem 2rem; border-radius: var(--radius); background: linear-gradient(135deg, var(--header-bg), #26357a); color: var(--header-text); }
.hero__title { margin: 0 0 0.75rem; font-size: clamp(2rem, 5vw, 3rem); letter-spacing: -0.02em; }
.hero__lead { max-width: 42rem; margin: 0 0 1.5rem; font-size: 1.2rem; color: #c9cfe3; }
.hero__actions { display: flex; flex-wrap: wrap; gap: 0.75rem; margin: 0; }
.hero .button { border-color: #c9cfe3; color: #fff; text-decoration: none; }
.hero .button:hover { background: #ffffff1a; }
.hero .button--solid { border-color: #93a4ff; background: #93a4ff; color: #11182b; }
.hero .button--solid:hover { background: #b3c0ff; }
a.button { display: inline-block; text-decoration: none; }
.page { max-width: var(--content); }
.layout--wide > main > h2 { margin-top: 2.5rem; }

/* ---------- 8. Footer ---------- */
.site-footer { border-top: 1px solid var(--border); background: var(--surface); font-size: 0.92rem; color: var(--muted); }
.site-footer__inner { display: flex; flex-wrap: wrap; gap: 0.5rem 2rem; justify-content: space-between; max-width: 76rem; margin: 0 auto; padding: 1.5rem 1.25rem; }
.site-footer ul { display: flex; flex-wrap: wrap; gap: 0.25rem 1.25rem; margin: 0; padding: 0; list-style: none; }
.site-footer a { color: var(--muted); }

/* Book banner (PL pages) */
.promo { margin-top: 1.5rem; }
.promo img { display: block; border: 1px solid var(--border); border-radius: 6px; }