/* PhysicsBase — indigo ink  and a brass seal. */
:root {
  --indigo: #121316; --indigo-deep: #15171c; --indigo-soft: #fff6c4;
  --paper: #ffffff; --surface: #ffffff; --ink: #121316; --slate: #5b5f6b; --line: #e2e4ea;
  --brass: #9a6b00; --brass-bright: #ffe14a; --brass-soft: #fff6c4;
  --danger: #d6331f; --danger-soft: #fde9e6; --ok: #10935f; --ok-soft: #e1f4ea;
  --code-bg: #15171c; --code-ink: #e6e8ee; --on-indigo: #ffffff; --marker: #ffe14a;
  --radius-s: 0px; --radius-m: 0px;
  --display: 'Host Grotesk', ui-sans-serif, system-ui, sans-serif;
  --sans: 'Host Grotesk', ui-sans-serif, system-ui, -apple-system, 'Segoe UI', sans-serif;
  --mono: 'Geist Mono', ui-monospace, SFMono-Regular, Menlo, monospace;
  --focus: 0 0 0 2px var(--ink);
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --indigo: #ffe14a; --indigo-deep: #0c0d10; --indigo-soft: #2b2610;
    --paper: #0f1013; --surface: #17191e; --ink: #eef0f4; --slate: #a2a7b3; --line: #2a2d35;
    --brass: #ffe14a; --brass-soft: #2b2610; --danger: #ff6b5a; --danger-soft: #3a1714; --ok: #4fd69c; --ok-soft: #12301f;
    --code-bg: #0c0d10; --on-indigo: #121316; color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --indigo: #ffe14a; --indigo-deep: #0c0d10; --indigo-soft: #2b2610;
  --paper: #0f1013; --surface: #17191e; --ink: #eef0f4; --slate: #a2a7b3; --line: #2a2d35;
  --brass: #ffe14a; --brass-soft: #2b2610; --danger: #ff6b5a; --danger-soft: #3a1714; --ok: #4fd69c; --ok-soft: #12301f;
  --code-bg: #0c0d10; --on-indigo: #121316; color-scheme: dark;
}

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; background: var(--paper); color: var(--ink); font: 400 1rem/1.55 var(--sans); }
img, svg { display: block; max-width: 100%; }
a { color: var(--indigo); text-underline-offset: 0.18em; }
a:hover { text-decoration-thickness: 2px; }
:focus-visible { outline: none; box-shadow: var(--focus); border-radius: 4px; }
h1, h2, h3 { line-height: 1.12; margin: 0; letter-spacing: -0.015em; text-wrap: balance; }
h1, .panel h2 { font-family: var(--display); font-weight: 800; letter-spacing: -0.04em; }
p { margin: 0; }
code, pre, kbd { font-family: var(--mono); font-size: 0.875em; }
.wrap { width: min(1120px, 100% - 32px); margin-inline: auto; }
.visually-hidden { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }

/* ---- buttons & inputs ---- */
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 0.5rem;
  min-height: 44px; padding: 0.6rem 1.2rem; border-radius: 0; box-shadow: 3px 3px 0 var(--marker);
  font: 500 1rem/1 var(--sans); text-decoration: none; cursor: pointer;
  border: 1px solid var(--indigo); background: var(--indigo); color: var(--on-indigo);
}
.btn { transition: transform .25s cubic-bezier(.3,1.5,.5,1), background .2s; }
.btn:hover { background: color-mix(in srgb, var(--indigo) 88%, black); transform: translateY(-1px); }
.btn:active { transform: scale(.97); }
.btn.secondary { background: transparent; color: var(--indigo); }
.btn.secondary:hover { background: var(--indigo-soft); }
.btn.danger { background: transparent; color: var(--danger); border-color: color-mix(in srgb, var(--danger) 45%, transparent); }
.btn.danger:hover { background: var(--danger-soft); }
.btn.ok { background: var(--ok); border-color: var(--ok); color: var(--on-indigo); }
.btn.small { min-height: 34px; padding: 0.35rem 0.75rem; font-size: 0.9rem; }
.btn[disabled] { opacity: 0.55; cursor: progress; }
.btn.full { width: 100%; }

label { display: block; font-weight: 500; margin-bottom: 0.35rem; }
.hint { color: var(--slate); font-size: 0.9rem; margin-top: 0.3rem; }
input[type="text"], input[type="email"], input[type="url"], input[type="number"], input[type="search"], input[type="password"], select, textarea {
  width: 100%; min-height: 44px; padding: 0.6rem 0.75rem; border-radius: var(--radius-s);
  border: 1px solid var(--line); background: var(--surface); color: var(--ink); font: inherit;
}
input:focus-visible, select:focus-visible, textarea:focus-visible { border-color: var(--brass); }
.field { margin-bottom: 1.1rem; }
.check { display: flex; gap: 0.6rem; align-items: flex-start; font-weight: 400; }
.check input { margin-top: 0.3rem; width: 18px; height: 18px; accent-color: var(--indigo); }

.notice { padding: 0.75rem 1rem; border-radius: var(--radius-s); background: var(--indigo-soft); margin: 1rem 0; }
.notice.error { background: var(--danger-soft); color: var(--danger); }
.notice.dev { background: var(--brass-soft); color: var(--ink); }
.notice:empty { display: none; }

/* ---- top bar ---- */
.topbar { position: sticky; top: 0; z-index: 10; border-bottom: 1px solid var(--line); background: color-mix(in srgb, var(--paper) 75%, transparent); backdrop-filter: blur(14px); -webkit-backdrop-filter: blur(14px); }
.topbar .wrap { display: flex; align-items: center; justify-content: space-between; gap: 1rem; min-height: 64px; }
.brand { display: inline-flex; align-items: center; gap: 0.55rem; font: 800 1.1rem var(--display); color: var(--ink); text-decoration: none; letter-spacing: -0.03em; }
.brand img { display: block; width: 26px; height: 26px; image-rendering: pixelated; }
.topnav { display: flex; gap: 1.25rem; align-items: center; }
.topnav a:not(.btn) { color: var(--ink); text-decoration: none; }
.topnav a:not(.btn):hover { color: var(--indigo); text-decoration: underline; }
@media (max-width: 640px) { .topnav .hide-sm { display: none; } }

/* ---- code ---- */
pre.code {
  margin: 0; padding: 1.1rem 1.2rem; overflow-x: auto; border-radius: var(--radius-m);
  background: var(--code-bg); color: var(--code-ink); line-height: 1.6; font-size: 0.86rem;
}
pre.code .c { color: #8a92c4; }
pre.code .s { color: #f0c873; }
pre.code .k { color: #a9b5ff; }

@media (prefers-reduced-motion: reduce) { *, *::before, *::after { animation: none !important; transition: none !important; } }