:root {
  color-scheme: light dark;
  --bg: #ffffff;
  --text: #16181d;
  --muted: #666d7a;
  --line: #e4e6ea;
  --hover: #f5f6f8;
  --accent: #1f4fd8;
  --error: #b42318;
  --good: #137a45;
  --heat-1: #c6d4f7;
  --heat-2: #8ea9ee;
  --heat-3: #4f76e2;
  --heat-4: #1f4fd8;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #111317;
    --text: #eceef2;
    --muted: #9aa1ae;
    --line: #2a2e36;
    --hover: #1a1d23;
    --accent: #8fb0ff;
    --error: #ff8a7a;
    --good: #66d19e;
    --heat-1: #24345f;
    --heat-2: #34508f;
    --heat-3: #5a7fd0;
    --heat-4: #8fb0ff;
  }
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  font-size: 16px;
  line-height: 1.5;
}

a {
  color: inherit;
  text-decoration: none;
}

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

.site-header {
  max-width: 720px;
  margin: 0 auto;
  padding: 24px 16px 0;
  border-bottom: 1px solid var(--line);
}

.brand {
  display: inline-block;
  margin-bottom: 16px;
  font-weight: 600;
}

.tabs {
  display: flex;
  gap: 24px;
  overflow-x: auto;
  font-size: 14px;
  color: var(--muted);
}

.tabs a {
  padding-bottom: 10px;
  border-bottom: 2px solid transparent;
  margin-bottom: -1px;
  white-space: nowrap;
}

.tabs a:hover {
  color: var(--text);
}

.tabs a[aria-current="page"] {
  border-bottom-color: var(--accent);
  color: var(--text);
}

.tab-end {
  margin-left: auto;
}

main {
  max-width: 720px;
  margin: 0 auto;
  padding: 48px 16px;
}

h1 {
  margin: 0;
  font-size: 32px;
  font-weight: 600;
  letter-spacing: -0.02em;
  line-height: 1.2;
}

.lead {
  margin: 8px 0 40px;
  color: var(--muted);
}

.lead a {
  color: var(--accent);
}

.subject-list {
  margin: 0;
  padding: 0;
  list-style: none;
  border-top: 1px solid var(--line);
}

.subject-list li {
  border-bottom: 1px solid var(--line);
}

.subject-list a {
  display: flex;
  flex-wrap: wrap;
  gap: 4px 16px;
  align-items: baseline;
  padding: 18px 8px;
}

.subject-list a:hover {
  background: var(--hover);
}

.code {
  min-width: 84px;
  font-weight: 600;
}

.name {
  flex: 1;
}

.count {
  font-size: 14px;
  color: var(--muted);
}

.empty {
  padding: 32px 0;
  border-top: 1px solid var(--line);
  color: var(--muted);
}

h2 {
  margin: 48px 0 16px;
  font-size: 18px;
  font-weight: 600;
}

.upload-form {
  display: grid;
  gap: 20px;
}

.upload-form label {
  display: grid;
  gap: 6px;
  font-size: 14px;
  font-weight: 500;
}

.upload-form input,
.upload-form select {
  width: 100%;
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--bg);
  color: var(--text);
  font: inherit;
}

.upload-form button {
  justify-self: start;
  padding: 10px 20px;
  border: 0;
  border-radius: 6px;
  background: var(--accent);
  color: var(--bg);
  font: inherit;
  font-weight: 500;
  cursor: pointer;
}

.upload-form :focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.notice {
  margin: 0 0 24px;
  padding: 12px 14px;
  border: 1px solid var(--line);
  border-radius: 6px;
}

.notice-error {
  border-color: var(--error);
  color: var(--error);
}

.crumb {
  margin: 0 0 8px;
  font-size: 14px;
  color: var(--muted);
}

.crumb a:hover {
  color: var(--text);
}

.prose {
  overflow-wrap: anywhere;
}

.prose p:first-child {
  margin-top: 0;
}

.prose p:last-child {
  margin-bottom: 0;
}

.prose pre,
.test-output {
  overflow-x: auto;
  padding: 12px 14px;
  border-radius: 6px;
  background: var(--hover);
  font-size: 14px;
  line-height: 1.45;
}

code {
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 0.92em;
}

.figure {
  display: block;
  max-width: 100%;
  height: auto;
  margin: 16px 0;
  border-radius: 6px;
  background: #ffffff;
}

.part {
  margin-top: 32px;
  padding-top: 24px;
  border-top: 1px solid var(--line);
}

.part-head {
  display: flex;
  gap: 16px;
  align-items: baseline;
  justify-content: space-between;
  margin-bottom: 12px;
}

.part .answer {
  width: 100%;
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--bg);
  color: var(--text);
  font: inherit;
}

.part .answer:focus-visible,
.part button:focus-visible,
.self-points:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.code-input {
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace !important;
  font-size: 14px !important;
  line-height: 1.45;
  tab-size: 4;
  white-space: pre;
  overflow-x: auto;
}

.input-hint {
  margin: 6px 0 0;
  font-size: 13px;
  color: var(--muted);
}

.katex-display {
  overflow-x: auto;
  overflow-y: hidden;
}

.choices {
  display: grid;
  gap: 8px;
}

.choices label {
  display: flex;
  gap: 8px;
  align-items: baseline;
}

.part-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 12px;
}

.secondary-button {
  padding: 10px 14px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--bg);
  color: var(--text);
  font: inherit;
  cursor: pointer;
}

.secondary-button:hover:not(:disabled) {
  background: var(--hover);
}

.secondary-button:disabled {
  color: var(--muted);
  cursor: default;
}

.feedback {
  min-height: 24px;
  margin-top: 12px;
  font-size: 14px;
  color: var(--muted);
}

.feedback[data-tone="good"],
.test-results [data-tone="good"] {
  color: var(--good);
}

.feedback[data-tone="bad"],
.test-results [data-tone="bad"] {
  color: var(--error);
}

.test-results {
  margin: 12px 0;
  padding: 0;
  list-style: none;
  font-size: 14px;
}

.test-results li {
  padding: 3px 0;
  overflow-wrap: anywhere;
}

.reveal {
  margin-top: 12px;
  padding: 12px 14px;
  border-left: 3px solid var(--accent);
  background: var(--hover);
}

.reveal.solution {
  border-left-color: var(--good);
}

.solution-label {
  margin: 0 0 8px;
  font-size: 13px;
  color: var(--muted);
}

.self-mark {
  display: grid;
  gap: 12px;
  margin-top: 12px;
}

.self-mark[hidden] {
  display: none;
}

.self-mark label {
  display: grid;
  gap: 6px;
  max-width: 200px;
  font-size: 14px;
}

.self-points {
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--bg);
  color: var(--text);
  font: inherit;
}

.self-mark .primary-button {
  justify-self: start;
}

.pager {
  display: flex;
  justify-content: space-between;
  margin-top: 40px;
  padding-top: 16px;
  border-top: 1px solid var(--line);
  font-size: 14px;
  color: var(--muted);
}

.pager a:hover {
  color: var(--text);
}

.header-top {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
}

.header-top form {
  margin: 0;
}

.link-button {
  padding: 0;
  border: 0;
  background: none;
  color: var(--muted);
  font: inherit;
  font-size: 14px;
  cursor: pointer;
}

.link-button:hover {
  color: var(--text);
}

.primary-button {
  padding: 10px 20px;
  border: 0;
  border-radius: 6px;
  background: var(--accent);
  color: var(--bg);
  font: inherit;
  font-weight: 500;
  cursor: pointer;
}

.link-value {
  overflow-wrap: anywhere;
}

.stats {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(130px, 1fr));
  gap: 16px;
  margin: 0 0 32px;
}

.stats dt {
  font-size: 14px;
  color: var(--muted);
}

.stats dd {
  margin: 2px 0 0;
  font-size: 24px;
  font-weight: 600;
}

.heatmap-scroll {
  overflow-x: auto;
}

.heatmap {
  display: flex;
  gap: 3px;
  width: max-content;
}

.heatmap-week {
  display: grid;
  grid-template-rows: 16px repeat(7, 10px);
  gap: 3px;
}

.heatmap-month {
  width: 10px;
  font-size: 11px;
  line-height: 14px;
  color: var(--muted);
  white-space: nowrap;
}

.cell {
  display: inline-block;
  width: 10px;
  height: 10px;
  border-radius: 2px;
  background: var(--line);
}

.cell.future {
  visibility: hidden;
}

.level-1 { background: var(--heat-1); }
.level-2 { background: var(--heat-2); }
.level-3 { background: var(--heat-3); }
.level-4 { background: var(--heat-4); }

.legend {
  display: flex;
  gap: 3px;
  align-items: center;
  justify-content: flex-end;
  margin: 8px 0 0;
  font-size: 12px;
  color: var(--muted);
}

.results,
.stored {
  margin: 0 0 32px;
  padding: 0;
  list-style: none;
  font-size: 14px;
}

.results li,
.stored li {
  display: flex;
  flex-wrap: wrap;
  gap: 4px 16px;
  justify-content: space-between;
  padding: 10px 0;
  border-bottom: 1px solid var(--line);
  overflow-wrap: anywhere;
}