:root {
  color-scheme: light;
  --surface: #fcfcfb;
  --panel: #ffffff;
  --text: #0b0b0b;
  --text-secondary: #52514e;
  --border: #dddcd6;
  --land: #f1f0ec;
  --state-line: #d3d2cb;
  --dot: #a09f98;
  --idle: #c9c8c1;
  --blue: #2a78d6;
  --blue-light: #86b6ef;
  --blue-soft: #cde2fb;
  --blue-dark: #104281;
  --orange: #eb6834;
  --orange-soft: #fde9df;
  --code-keyword: #4a3aa7;
  --code-type: #104281;
  --code-string: #006e00;
  --code-number: #a8480f;
  --code-comment: #6b6a66;
}

* {
  box-sizing: border-box;
}

[hidden] {
  display: none !important;
}

body {
  margin: 0;
  padding: 20px 16px 32px;
  background: var(--surface);
  color: var(--text);
  font: 15px/1.45 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
}

header,
main,
.explanation {
  max-width: 1120px;
  margin-left: auto;
  margin-right: auto;
}

header {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 8px 24px;
  margin-bottom: 20px;
}

h1 {
  margin: 0;
  font-size: 24px;
}

h2 {
  margin: 0;
  font-size: 20px;
}

nav {
  display: flex;
  gap: 16px;
}

nav a {
  padding-bottom: 2px;
  color: var(--text-secondary);
  text-decoration: none;
  border-bottom: 2px solid transparent;
}

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

nav a[aria-current="page"] {
  color: var(--text);
  font-weight: 600;
  border-bottom-color: var(--text);
}

main.planner {
  display: grid;
  grid-template-columns: 340px minmax(0, 1fr);
  gap: 24px;
  align-items: start;
}

/* Forms */

form {
  display: grid;
  gap: 8px;
}

form.inline {
  grid-template-columns: minmax(0, 340px) 96px;
  gap: 16px;
}

/* A dropdown that opens to folders */

.dropdown {
  width: 100%;
  padding: 8px 10px;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--panel);
  color: var(--text);
  font: inherit;
  text-align: left;
  cursor: pointer;
}

.dropdown::after {
  content: "▾";
  float: right;
  color: var(--text-secondary);
}

.menu {
  position: absolute;
  z-index: 10;
  left: 0;
  right: 0;
  top: 100%;
  margin-top: 4px;
  padding: 4px;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--panel);
  box-shadow: 0 6px 18px rgb(0 0 0 / 0.16);
  max-height: 420px;
  overflow-y: auto;
}

.menu summary {
  display: flex;
  justify-content: space-between;
  padding: 6px 8px;
  border-radius: 4px;
  cursor: pointer;
}

.menu summary::before {
  content: "▸";
  width: 1.2em;
  color: var(--text-secondary);
}

.menu details[open] > summary::before {
  content: "▾";
}

.menu summary:hover,
.menu li button:hover {
  background: var(--blue-soft);
}

.menu summary .count {
  margin-left: auto;
  color: var(--text-secondary);
  font-variant-numeric: tabular-nums;
}

.menu ul {
  margin: 0 0 4px;
  padding: 0 0 0 1.2em;
  list-style: none;
}

.menu li button {
  width: 100%;
  padding: 5px 8px;
  border: 0;
  border-radius: 4px;
  background: none;
  color: inherit;
  font: inherit;
  text-align: left;
  cursor: pointer;
}

.menu .code {
  font-weight: 600;
}

.field {
  position: relative;
}

label,
.label {
  display: block;
  font-weight: 600;
  font-size: 13px;
  margin-bottom: 2px;
}

input[type="text"],
input[type="number"],
select {
  width: 100%;
  padding: 8px 10px;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--panel);
  color: var(--text);
  font: inherit;
}

input:focus-visible,
select:focus-visible,
button:focus-visible,
a:focus-visible {
  outline: 2px solid var(--blue);
  outline-offset: 1px;
}

.swap {
  justify-self: end;
  margin: -4px 0 -12px;
  width: 32px;
  height: 28px;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--panel);
  color: var(--text-secondary);
  font-size: 16px;
  line-height: 1;
  cursor: pointer;
}

.swap:disabled,
.example:disabled {
  cursor: default;
  opacity: 0.5;
}

.example {
  justify-self: start;
  margin-top: 4px;
  padding: 4px 10px;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--panel);
  color: var(--text-secondary);
  font: inherit;
  font-size: 13px;
  cursor: pointer;
}

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

.options {
  position: absolute;
  z-index: 10;
  left: 0;
  right: 0;
  top: 100%;
  margin: 4px 0 0;
  padding: 4px;
  list-style: none;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--panel);
  box-shadow: 0 6px 18px rgb(0 0 0 / 0.16);
  max-height: 320px;
  overflow-y: auto;
}

.options li {
  padding: 6px 8px;
  border-radius: 4px;
  cursor: pointer;
}

.options li[aria-selected="true"] {
  background: var(--blue-soft);
}

.options .code {
  font-weight: 600;
}

.options .name {
  display: block;
  color: var(--text-secondary);
  font-size: 12px;
}

.mode {
  display: flex;
  gap: 16px;
  margin: 4px 0 0;
  padding: 0;
  border: 0;
}

.mode legend {
  padding: 0;
  font-weight: 600;
  font-size: 13px;
}

.mode label {
  font-weight: 400;
  font-size: 15px;
  cursor: pointer;
}

/* Result */

.result {
  margin-top: 20px;
}

.result p {
  margin: 0;
  font-size: 17px;
}

.result ol {
  margin: 10px 0 0;
  padding: 0;
  list-style: none;
}

.result li {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  padding: 6px 0;
  border-top: 1px solid var(--border);
  font-variant-numeric: tabular-nums;
}

.result .leg {
  font-weight: 600;
}

/* Maps */

.map-panel,
.chart-panel {
  position: relative;
}

.map {
  display: block;
  width: 100%;
  height: auto;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--panel);
}

.map .land {
  fill: var(--land);
  stroke: var(--state-line);
  stroke-width: 1;
  stroke-linejoin: round;
  vector-effect: non-scaling-stroke;
}

.map .airport,
.map .dot {
  fill: var(--dot);
  fill-opacity: 0.75;
}

.map .airport {
  cursor: pointer;
}

.map .airport:hover {
  fill: var(--blue);
  fill-opacity: 1;
}

.map .settled {
  fill: var(--blue);
  fill-opacity: 0.9;
}

.map .frontier {
  fill: var(--orange);
  fill-opacity: 1;
}

.map .tree,
.map .relax,
.map .route-line {
  fill: none;
  stroke-linejoin: round;
  stroke-linecap: round;
  vector-effect: non-scaling-stroke;
}

.map .tree {
  stroke: var(--blue-light);
  stroke-width: 1;
  stroke-opacity: 0.55;
}

.map .relax {
  stroke: var(--text);
  stroke-width: 1.5;
}

.map .route-line {
  stroke: var(--blue);
  stroke-width: 2.5;
}

.map .stop,
.map .mark {
  fill: var(--blue);
  stroke: var(--panel);
  stroke-width: 2;
  vector-effect: non-scaling-stroke;
}

.map .stop {
  cursor: pointer;
}

.map .mark.current {
  fill: var(--text);
}

.map .mark.neighbor {
  fill: var(--panel);
  stroke: var(--text);
}

.map text {
  fill: var(--text);
  font-weight: 600;
  stroke: var(--panel);
  stroke-linejoin: round;
  paint-order: stroke;
  pointer-events: none;
}

.tooltip {
  position: absolute;
  z-index: 5;
  max-width: 260px;
  padding: 6px 8px;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--panel);
  box-shadow: 0 4px 12px rgb(0 0 0 / 0.16);
  font-size: 13px;
  pointer-events: none;
}

.tooltip .muted {
  display: block;
  color: var(--text-secondary);
}

/* Busiest-flights chart */

.chart-panel {
  margin-top: 16px;
}

.chart {
  margin: 8px 0 0;
  padding: 0;
  list-style: none;
}

.chart li {
  display: grid;
  grid-template-columns: minmax(120px, 220px) minmax(0, 1fr) 64px;
  align-items: center;
  gap: 12px;
  padding: 1px 0;
}

.chart .place {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.chart .track {
  display: block;
}

.chart .bar {
  display: block;
  height: 18px;
  border-radius: 0 4px 4px 0;
}

.chart .count {
  color: var(--text-secondary);
  font-variant-numeric: tabular-nums;
  text-align: right;
}

.short {
  background: var(--blue-light);
}

.medium {
  background: var(--blue);
}

.long {
  background: var(--blue-dark);
}

/* Explanation */

.explanation {
  margin-top: 40px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
}

.explanation > h2 {
  margin-bottom: 16px;
}

.card {
  margin-bottom: 16px;
  padding: 20px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--panel);
}

.card h3 {
  display: flex;
  align-items: center;
  gap: 10px;
  margin: 0 0 16px;
  font-size: 17px;
}

.card h4 {
  margin: 0 0 6px;
  font-size: 13px;
}

.aside {
  color: var(--text-secondary);
  font-weight: 400;
}

.card .note {
  margin: -8px 0 16px;
  color: var(--text-secondary);
  font-size: 13px;
}

.below {
  margin: 16px 0;
}

.step {
  flex: none;
  display: inline-grid;
  place-items: center;
  width: 26px;
  height: 26px;
  border-radius: 50%;
  background: var(--text);
  color: var(--panel);
  font-size: 14px;
}

.split {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);
  gap: 24px;
  align-items: start;
  margin-bottom: 16px;
}

.structures {
  display: grid;
  grid-template-columns: minmax(0, 3fr) minmax(0, 2fr);
  gap: 16px;
  margin-top: 16px;
}

/* Code, with a bar on the running line */

.code,
.csv {
  position: relative;
  max-height: 520px;
  overflow: auto;
  padding: 8px 0;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--surface);
  font: 12px/1.6 ui-monospace, "Cascadia Mono", Consolas, Menlo, monospace;
  white-space: pre;
}

.code > div,
.csv > span {
  display: block;
  width: max-content;
  min-width: 100%;
  padding: 0 12px 0 8px;
  border-left: 4px solid transparent;
}

.code .num {
  display: inline-block;
  width: 3ch;
  margin-right: 12px;
  color: var(--text-secondary);
  text-align: right;
  user-select: none;
}

.code > .running,
.csv > .running {
  border-left-color: var(--blue);
  background: var(--blue-soft);
}

.code .keyword {
  color: var(--code-keyword);
  font-weight: 600;
}

.code .type {
  color: var(--code-type);
}

.code .string {
  color: var(--code-string);
}

.code .number {
  color: var(--code-number);
}

.code .comment {
  color: var(--code-comment);
  font-style: italic;
}

.variables {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  min-height: 28px;
  margin-top: 12px;
  font: 12px/1.6 ui-monospace, "Cascadia Mono", Consolas, Menlo, monospace;
}

.variable {
  padding: 1px 8px;
  border: 1px solid var(--border);
  border-radius: 4px;
  background: var(--surface);
}

.variable .name {
  color: var(--text-secondary);
}

.legend {
  display: flex;
  flex-wrap: wrap;
  gap: 4px 16px;
  margin: 8px 0 0;
  padding: 0;
  list-style: none;
  color: var(--text-secondary);
  font-size: 13px;
}

.legend li {
  display: flex;
  align-items: center;
  gap: 6px;
}

.key {
  display: inline-block;
  width: 10px;
  height: 10px;
  border-radius: 50%;
}

.key.dot {
  background: var(--dot);
}

.key.settled,
.key.match {
  background: var(--blue);
}

.key.frontier {
  background: var(--orange);
}

.key.untouched {
  background: var(--idle);
}

.key.seen {
  border: 2px solid var(--text);
}

.key.c0,
.key.c1,
.key.c2,
.key.c3,
.key.short,
.key.medium,
.key.long {
  border-radius: 2px;
}

/* AVL tree */

.sort-drawing {
  display: block;
  width: 100%;
  height: auto;
}

/* The tree is drawn at its natural size and scrolls sideways when a search
   reaches more nodes than fit. */
.tree-scroller {
  overflow-x: auto;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--surface);
}

.tree-drawing {
  display: block;
  margin: 8px auto;
}

.tree-drawing text {
  fill: var(--text-secondary);
  font-size: 10.5px;
  text-anchor: middle;
}

.tree-drawing text.seen,
.tree-drawing text.match {
  fill: var(--text);
  font-weight: 600;
}

.tree-drawing text.sub {
  font-size: 9px;
}

.tree-drawing line {
  stroke: var(--border);
  stroke-width: 1;
}

.tree-drawing line.seen,
.tree-drawing line.match {
  stroke: var(--text);
  stroke-width: 1.5;
}

.tree-drawing circle {
  fill: var(--idle);
}

.tree-drawing circle.seen {
  fill: var(--panel);
  stroke: var(--text);
  stroke-width: 2;
}

.tree-drawing circle.match {
  fill: var(--blue);
}

.tree-drawing circle.current {
  stroke: var(--orange);
  stroke-width: 3.5;
}

/* Merge sort */

.sort-drawing .bar {
  fill: var(--idle);
}

.sort-drawing .bar.active {
  fill: var(--blue);
}

/* Priority queue and hash table */

.queue-drawing {
  display: block;
  width: 100%;
  height: auto;
}

.queue-drawing line {
  stroke: var(--idle);
  stroke-width: 1.5;
}

.queue-drawing circle {
  fill: var(--orange-soft);
  stroke: var(--orange);
  stroke-width: 1.5;
}

.queue-drawing circle.root {
  stroke-width: 3.5;
}

.queue-drawing text {
  text-anchor: middle;
}

.queue-drawing .code-label {
  fill: var(--text);
  font-size: 10px;
  font-weight: 600;
}

.queue-drawing .priority {
  fill: var(--text-secondary);
  font-size: 8.5px;
}

.table-cells {
  display: flex;
  flex-wrap: wrap;
  gap: 2px;
  min-height: 12px;
}

.table-cells span {
  width: 6px;
  height: 9px;
  border-radius: 2px;
}

.c0 {
  background: var(--panel);
  box-shadow: inset 0 0 0 1px var(--border);
}

.c1 {
  background: var(--blue-light);
}

.c2 {
  background: var(--blue);
}

.c3 {
  background: var(--blue-dark);
}

/* Replay controls */

.player {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 6px;
}

.player button {
  flex: none;
  width: 36px;
  height: 32px;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--panel);
  color: var(--text);
  font-size: 13px;
  line-height: 1;
  cursor: pointer;
}

.player button:disabled,
.player input:disabled {
  cursor: default;
  opacity: 0.4;
}

.player input[type="range"] {
  flex: 1 1 120px;
  min-width: 80px;
  accent-color: var(--blue);
}

.player .readout {
  flex: none;
  min-width: 110px;
  color: var(--text-secondary);
  font-size: 13px;
  font-variant-numeric: tabular-nums;
  text-align: right;
}

@media (max-width: 800px) {
  main.planner,
  .split,
  .structures {
    grid-template-columns: minmax(0, 1fr);
  }

  .card {
    padding: 16px;
  }

  .chart li {
    grid-template-columns: 96px minmax(0, 1fr) 56px;
    gap: 8px;
  }
}