:root {
  --ink: #1c1f24;
  --ink-soft: #4a525c;
  --line: #d9dde3;
  --paper: #ffffff;
  --paper-soft: #f6f7f9;
  --accent: #245b8a;
  --ok: #1e6b3a;
  --ok-bg: #edf7f0;
  --bad: #a23a2f;
  --bad-bg: #fbeeec;
  --serif: Georgia, "Times New Roman", "Noto Serif", serif;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, "Noto Sans", sans-serif;
  --mono: ui-monospace, "SFMono-Regular", Menlo, Consolas, "Liberation Mono", monospace;
}

* { box-sizing: border-box; }

html { background: var(--paper); color: var(--ink); }

body {
  margin: 0;
  font: 17px/1.55 var(--sans);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

a { color: var(--accent); }
a:hover { color: var(--ink); }

.site-header {
  display: flex;
  align-items: baseline;
  gap: 2rem;
  padding: 1rem clamp(1rem, 4vw, 3rem);
  border-bottom: 1px solid var(--line);
}

.brand {
  display: inline-flex;
  align-items: baseline;
  gap: 0.75rem;
  color: var(--ink);
  text-decoration: none;
}

.brand__mark {
  font: 700 1.6rem/1 var(--serif);
  letter-spacing: -0.02em;
}

.brand__mark sup { font-size: 0.7em; color: var(--accent); }

.brand__text {
  font-size: 0.85rem;
  color: var(--ink-soft);
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.site-nav { flex: 1; }
.site-nav a { text-decoration: none; font-weight: 600; }
.site-nav a + a { margin-left: 1.25rem; }

.site-actions {
  display: inline-flex;
  align-items: center;
  gap: 1rem;
  align-self: center;
}

.site-actions form { margin: 0; }

.logout button {
  font-size: 0.85rem;
  padding: 0.2rem 0.7rem;
}

.language {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.85rem;
  color: var(--ink-soft);
}

.language button {
  font: inherit;
  padding: 0.2rem 0.55rem;
  border: 1px solid var(--line);
  border-radius: 4px;
  background: var(--paper);
  color: var(--accent);
  cursor: pointer;
}

.language__current { font-weight: 700; }

.content {
  flex: 1;
  width: min(52rem, 100% - 2rem);
  margin: 0 auto;
  padding: 1.5rem 0 3rem;
}

h1, h2 { font-family: var(--serif); font-weight: 600; line-height: 1.2; }
h1 { font-size: 1.9rem; margin: 0.5rem 0 1rem; }
h2 { font-size: 1.25rem; margin: 1.5rem 0 0.75rem; }

.lead { color: var(--ink-soft); margin-top: 0; }
.breadcrumbs { font-size: 0.9rem; color: var(--ink-soft); margin: 0; }

.catalog { list-style: none; padding: 0; margin: 1rem 0; }

.catalog__item {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1.5rem;
  padding: 1rem 0;
  border-top: 1px solid var(--line);
}

.catalog__item:last-child { border-bottom: 1px solid var(--line); }
.catalog__item h2 { margin: 0 0 0.25rem; }
.catalog__item p { margin: 0; color: var(--ink-soft); }

button, .button {
  font: 600 1rem var(--sans);
  padding: 0.5rem 1.1rem;
  border: 1px solid var(--accent);
  border-radius: 4px;
  background: var(--accent);
  color: #fff;
  cursor: pointer;
  white-space: nowrap;
}

button:hover { filter: brightness(1.1); }
button:disabled { cursor: not-allowed; opacity: 0.5; }
button.secondary, .button.secondary { background: var(--paper); color: var(--accent); }
a.button { display: inline-block; text-decoration: none; }

.confirm {
  max-width: 40rem;
  padding: 1.25rem 1.5rem;
  border: 1px solid var(--line);
  border-left: 3px solid var(--accent);
  border-radius: 4px;
}

.confirm p { margin: 0 0 0.75rem; }
.confirm__actions { display: flex; flex-wrap: wrap; align-items: center; gap: 1rem; margin-top: 1.25rem; }
.confirm__actions form { margin: 0; }

.statement {
  padding: 1.25rem 1.5rem;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--paper-soft);
}

.statement__text { margin: 0 0 0.75rem; font-family: var(--serif); font-size: 1.1rem; }

.math { overflow-x: auto; padding: 0.25rem 0; font-size: 1.1rem; }
.math mjx-container { margin: 0.5rem 0 !important; }

.math__fallback {
  border-collapse: collapse;
  font-family: var(--mono);
}

.math__fallback td { padding: 0.15rem 0.6rem; text-align: right; }
.math__fallback td.augmented { border-left: 1px solid var(--ink-soft); }
.math__fallback table { display: inline-table; margin-right: 1.5rem; vertical-align: middle; }
.math__fallback caption { caption-side: left; padding-right: 0.4rem; vertical-align: middle; }
.math[data-rendered] .math__fallback { display: none; }

.answer { margin-top: 1.5rem; }

.field {
  display: grid;
  gap: 0.35rem;
  padding: 0.75rem 0.9rem;
  margin: 0.5rem 0;
  border-left: 3px solid transparent;
  border-radius: 4px;
}

.field label { font-weight: 600; }
.field input, .field select, .field textarea {
  font: 1rem var(--sans);
  padding: 0.45rem 0.6rem;
  border: 1px solid var(--line);
  border-radius: 4px;
  background: var(--paper);
  color: var(--ink);
  max-width: 100%;
}

.field input { width: 18rem; }
.field select { width: max-content; }
.field textarea { font-family: var(--mono); line-height: 1.5; width: max-content; min-width: 14rem; resize: both; }
.field input:focus, .field select:focus, .field textarea:focus { outline: 2px solid var(--accent); outline-offset: 1px; }

.hint { color: var(--ink-soft); font-size: 0.85rem; }

.field--ok { border-left-color: var(--ok); background: var(--ok-bg); }
.field--bad { border-left-color: var(--bad); background: var(--bad-bg); }
.field--ok .outcome { color: var(--ok); }
.field--bad .outcome { color: var(--bad); }
.outcome { font-size: 0.9rem; font-weight: 600; }

.actions { display: flex; align-items: center; gap: 1.25rem; margin: 1rem 0 0 0.9rem; }
.attempts { color: var(--ink-soft); }

.summary { padding: 0.75rem 1rem; border-radius: 4px; margin: 1.25rem 0 0; font-weight: 600; }
.summary--ok { color: var(--ok); background: var(--ok-bg); }
.summary--bad { color: var(--bad); background: var(--bad-bg); }
.notice { color: var(--ink-soft); margin: 1rem 0 0; }

.replace { display: flex; flex-wrap: wrap; align-items: center; gap: 1.25rem; margin: 2rem 0 0; padding-top: 1.25rem; border-top: 1px solid var(--line); }
.replace .parameters { flex-basis: 100%; max-width: 30rem; }

.catalog__item form { flex: 0 0 23rem; display: flex; flex-direction: column; align-items: flex-end; gap: 0.5rem; }
.catalog__item form .parameters { align-self: stretch; }
.parameters summary { cursor: pointer; color: var(--ink-soft); font-size: 0.95rem; }
.parameters__field { display: flex; justify-content: space-between; align-items: center; gap: 0.75rem; margin: 0.4rem 0; font-size: 0.95rem; }
.parameters__field span { flex: 1; }
.parameters__field select { flex: 0 0 12.5rem; }
.parameters .hint { display: block; max-width: 24rem; }

.site-footer {
  padding: 1rem clamp(1rem, 4vw, 3rem);
  border-top: 1px solid var(--line);
  color: var(--ink-soft);
  font-size: 0.85rem;
}

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

@media (max-width: 600px) {
  .site-header { flex-wrap: wrap; gap: 0.75rem 1.5rem; }
  .catalog__item { flex-direction: column; align-items: flex-start; }
  .catalog__item form { flex-basis: auto; align-self: stretch; }
  .field input { width: 100%; }
}