/* Design language: a scholarly, paper-like page — warm paper background,
   bookish serif for prose, monospace for anything numeric, ink-blue accent.
   System fonts only: the page makes zero external requests. */

:root {
  --bg: #f8f6f1;
  --fg: #211e19;
  --muted: #6e6960;
  --faint: #a49d92;
  --card-bg: #fffefb;
  --card-border: #e7e2d7;
  --card-shadow: 0 1px 2px rgba(60, 50, 30, 0.04), 0 10px 28px -18px rgba(60, 50, 30, 0.2);
  --accent: #3a49b4;
  --accent-fg: #ffffff;
  --good: #1d7a48;
  --good-bg: rgba(29, 122, 72, 0.06);
  --good-border: rgba(29, 122, 72, 0.22);
  --bad: #b23a2e;
  --bad-bg: rgba(178, 58, 46, 0.1);
  --unknown: #948e83;
  --code-bg: #f1ede3;
  --selection: rgba(58, 73, 180, 0.18);
  --serif: "Iowan Old Style", "Palatino Linotype", "Book Antiqua", Georgia, serif;
  --sans: system-ui, -apple-system, "Segoe UI", sans-serif;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  color-scheme: light;
}

:root[data-theme="dark"] {
  --bg: #191817;
  --fg: #e9e6df;
  --muted: #a29b8f;
  --faint: #6f695f;
  --card-bg: #201f1d;
  --card-border: #35332f;
  --card-shadow: 0 1px 2px rgba(0, 0, 0, 0.35), 0 10px 28px -18px rgba(0, 0, 0, 0.6);
  --accent: #9aa5f5;
  --accent-fg: #14131c;
  --good: #55c082;
  --good-bg: rgba(85, 192, 130, 0.08);
  --good-border: rgba(85, 192, 130, 0.28);
  --bad: #e77362;
  --bad-bg: rgba(231, 115, 98, 0.12);
  --unknown: #767066;
  --code-bg: #282723;
  --selection: rgba(154, 165, 245, 0.28);
  color-scheme: dark;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #191817;
    --fg: #e9e6df;
    --muted: #a29b8f;
    --faint: #6f695f;
    --card-bg: #201f1d;
    --card-border: #35332f;
    --card-shadow: 0 1px 2px rgba(0, 0, 0, 0.35), 0 10px 28px -18px rgba(0, 0, 0, 0.6);
    --accent: #9aa5f5;
    --accent-fg: #14131c;
    --good: #55c082;
    --good-bg: rgba(85, 192, 130, 0.08);
    --good-border: rgba(85, 192, 130, 0.28);
    --bad: #e77362;
    --bad-bg: rgba(231, 115, 98, 0.12);
    --unknown: #767066;
    --code-bg: #282723;
    --selection: rgba(154, 165, 245, 0.28);
    color-scheme: dark;
  }
}

* { box-sizing: border-box; }

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

body {
  margin: 0 auto;
  padding: 2.75rem 1.25rem 4rem;
  max-width: 52rem;
  background: var(--bg);
  color: var(--fg);
  font: 17px/1.65 var(--serif);
}

a { color: var(--accent); text-decoration-thickness: 1px; text-underline-offset: 2px; }
a:hover { text-decoration-thickness: 2px; }

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
  border-radius: 4px;
}

code, pre, .value, #expr { font-family: var(--mono); }
code {
  background: var(--code-bg);
  padding: 0.1em 0.35em;
  border-radius: 4px;
  font-size: 0.82em;
}

/* --- header --- */
header { position: relative; }

.theme-toggle {
  position: absolute;
  top: -1.35rem;
  /* Stay aligned with the viewport edge on wide screens, like the reference
     page, while falling back to the content edge on narrow screens. */
  right: min(0rem, calc(50% - 50vw + 2rem));
  display: grid;
  place-items: center;
  width: 2.35rem;
  height: 2.35rem;
  padding: 0;
  border: 1px solid var(--card-border);
  border-radius: 999px;
  background: var(--card-bg);
  color: var(--muted);
  font: 1rem/1 var(--sans);
  cursor: pointer;
  transition: color 0.15s, border-color 0.15s, background-color 0.15s,
              transform 0.15s;
}
.theme-toggle:hover {
  color: var(--fg);
  border-color: var(--muted);
  transform: rotate(12deg);
}
.theme-toggle:active { transform: rotate(12deg) scale(0.94); }

h1 {
  margin: 0 0 0.35rem;
  padding-right: 3rem;
  font-size: 2.6rem;
  font-weight: 600;
  letter-spacing: -0.015em;
  line-height: 1.15;
}
.tagline { margin: 0.4rem 0; color: var(--muted); max-width: 44rem; }

.pi-strip {
  margin-top: 1.4rem;
  font-family: var(--mono);
  font-size: 0.72rem;
  letter-spacing: 0.12em;
  color: var(--faint);
  white-space: nowrap;
  overflow: hidden;
  user-select: none;
  -webkit-mask-image: linear-gradient(to right, black 55%, transparent 98%);
  mask-image: linear-gradient(to right, black 55%, transparent 98%);
}

h2 {
  margin: 3rem 0 0.85rem;
  font-size: 1.5rem;
  font-weight: 600;
  letter-spacing: -0.01em;
}
h2::before {
  content: "";
  display: block;
  width: 2.5rem;
  height: 2px;
  background: var(--accent);
  opacity: 0.55;
  margin-bottom: 0.65rem;
}

/* --- example chips --- */
.chips { display: flex; flex-wrap: wrap; gap: 0.5rem; margin-top: 1.6rem; }
.chip {
  padding: 0.32rem 0.8rem;
  font-size: 0.84rem;
  font-family: var(--mono);
  border: 1px solid var(--card-border);
  border-radius: 999px;
  background: var(--card-bg);
  color: var(--fg);
  cursor: pointer;
  transition: border-color 0.15s, color 0.15s, box-shadow 0.15s;
}
.chip:hover {
  border-color: var(--accent);
  color: var(--accent);
  box-shadow: 0 2px 8px -4px var(--selection);
}

/* --- input row --- */
#repl-form { display: flex; gap: 0.55rem; margin: 1rem 0 0.3rem; }
#expr {
  flex: 1;
  min-width: 0;
  padding: 0.7rem 0.95rem;
  font-size: 1.05rem;
  border: 1.5px solid var(--card-border);
  border-radius: 10px;
  background: var(--card-bg);
  color: var(--fg);
  transition: border-color 0.15s, box-shadow 0.15s;
}
#expr::placeholder { color: var(--faint); }
#expr:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--selection);
}
#repl-form button {
  padding: 0.7rem 1.2rem;
  font: 600 0.95rem var(--sans);
  border: none;
  border-radius: 10px;
  background: var(--accent);
  color: var(--accent-fg);
  cursor: pointer;
  transition: filter 0.15s, transform 0.05s;
}
#repl-form button:hover { filter: brightness(1.12); }
#repl-form button:active { transform: translateY(1px); }
.hint {
  margin: 0.45rem 0 1.5rem;
  font: 0.82rem var(--sans);
  color: var(--muted);
}

/* --- busy bar --- */
#busy {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  margin-bottom: 1rem;
  padding: 0.5rem 0.9rem;
  border: 1px solid var(--card-border);
  border-radius: 10px;
  background: var(--card-bg);
  font: 0.88rem var(--sans);
  color: var(--muted);
}
#busy[hidden] { display: none; }
#busy button {
  margin-left: auto;
  padding: 0.22rem 0.75rem;
  font: 0.82rem var(--sans);
  border: 1px solid var(--bad);
  border-radius: 7px;
  background: transparent;
  color: var(--bad);
  cursor: pointer;
}
#busy button:hover { background: var(--bad-bg); }
.spinner {
  width: 0.9em;
  height: 0.9em;
  border: 2px solid var(--card-border);
  border-top-color: var(--accent);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }

/* --- result cards --- */
#results { display: flex; flex-direction: column; gap: 1.1rem; }
.card {
  border: 1px solid var(--card-border);
  border-radius: 12px;
  background: var(--card-bg);
  box-shadow: var(--card-shadow);
  padding: 1.05rem 1.3rem 1.15rem;
  animation: card-in 0.25s ease-out;
}
@keyframes card-in {
  from { opacity: 0; transform: translateY(6px); }
}
.card-expr {
  font-family: var(--mono);
  font-size: 1.02rem;
  word-break: break-all;
  padding-bottom: 0.8rem;
  margin-bottom: 0.95rem;
  border-bottom: 1px solid var(--card-border);
}
.card-error { color: var(--bad); font: 0.92rem var(--sans); }

.panes {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1.15rem;
}
@media (max-width: 40rem) { .panes { grid-template-columns: 1fr; } }

.pane { min-width: 0; }
.pane-label {
  font: 600 0.68rem var(--sans);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--muted);
  margin-bottom: 0.4rem;
}
.value {
  display: block;
  font-size: 1.02rem;
  line-height: 1.55;
  word-break: break-all;
  overflow-wrap: anywhere;
  max-height: 14rem;
  overflow-y: auto;
  scrollbar-width: thin;
  padding: 0.5rem 0.7rem;
  border-radius: 8px;
  background: var(--code-bg);
  border: 1px solid transparent;
}
.cr-value {
  background: var(--good-bg);
  border-color: var(--good-border);
}
.value .wrong { color: var(--bad); background: var(--bad-bg); border-radius: 3px; }
.value .unverified { color: var(--unknown); }

.verdict { font: 0.82rem/1.5 var(--sans); margin-top: 0.45rem; color: var(--muted); }
.verdict.good { color: var(--good); }
.verdict.bad { color: var(--bad); }

.digits-control {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin-top: 0.55rem;
  font: 0.82rem var(--sans);
  color: var(--muted);
}
.digits-value {
  min-width: 3.2em;
  font-family: var(--mono);
  color: var(--fg);
}
.digits-slider { flex: 1; max-width: 14rem; accent-color: var(--accent); }

/* --- representation --- */
details.repr {
  margin-top: 1rem;
  border-top: 1px solid var(--card-border);
  padding-top: 0.7rem;
}
details.repr summary {
  cursor: pointer;
  font: 0.86rem var(--sans);
  color: var(--muted);
  user-select: none;
}
details.repr summary:hover { color: var(--accent); }
.repr-label { font: 0.78rem var(--sans); color: var(--muted); margin: 0.65rem 0 0.25rem; }
.repr pre, .repr .pp {
  margin: 0;
  padding: 0.6rem 0.75rem;
  background: var(--code-bg);
  border-radius: 8px;
  font-family: var(--mono);
  font-size: 0.8rem;
  line-height: 1.45;
  overflow-x: auto;
  white-space: pre-wrap;
  word-break: break-all;
}

/* --- DAG tree --- */
.dag {
  padding: 0.65rem 0.8rem;
  background: var(--code-bg);
  border-radius: 8px;
  font-family: var(--mono);
  font-size: 0.82rem;
  line-height: 1.6;
  overflow: auto;
  max-height: 26rem;
  scrollbar-width: thin;
}
.dag details, .dag .dag-leaf { margin: 0; }
.dag .dag-children {
  margin-left: 0.55rem;
  padding-left: 0.7rem;
  border-left: 1px solid var(--card-border);
}
.dag .dag-children.dag-flat {
  margin-left: 0;
  padding-left: 0;
  border-left: none;
}
/* Space out siblings under a branching node, so the end of one child's
   chain is visually separated from the next child. */
.dag .dag-children:not(.dag-flat) > * + * { margin-top: 0.45rem; }
.dag .dag-chain-arrow { color: var(--unknown); }
.dag summary { cursor: pointer; list-style-position: inside; }
.dag .dag-leaf { padding-left: 1.35rem; }
.dag .dag-op { font-weight: 600; }
.dag .dag-appr { color: var(--good); }
.dag .dag-appr.dag-unevaluated { color: var(--unknown); font-style: italic; }
.dag .dag-shared { color: var(--muted); font-style: italic; }

/* --- explanation sections --- */
.explain { max-width: 44rem; }
.explain p, .explain li { color: var(--fg); }
.explain ul { padding-left: 1.3rem; }
.explain li { margin: 0.45rem 0; }
.explain sup { font-size: 0.7em; }
.explain strong { font-weight: 600; }

footer {
  margin-top: 3.5rem;
  padding-top: 1.25rem;
  border-top: 1px solid var(--card-border);
  font: 0.85rem var(--sans);
  color: var(--muted);
}

@media (prefers-reduced-motion: reduce) {
  .card { animation: none; }
  .chip, #expr, #repl-form button, .theme-toggle { transition: none; }
}