:root {
  color-scheme: light dark;
  --page: #faf8f2;
  --paper: #fff;
  --ink: #24211c;
  --muted: #6c665b;
  --line: #ddd7c9;
  --accent: #806000;
  --primary: #f4c430;
  --primary-hover: #e2b325;
  --wash: #fff4cc;
  --surface-hover: #f4f0e6;
  --gutter: #f7f4eb;
  --selection: #f8df83;
  --control-border: #948975;
  --error: #a12424;
  --code-font: ui-monospace, SFMono-Regular, Consolas, monospace;
  --primary-ink: #24211c;
  --selection-ink: var(--ink);
  --syntax-keyword: #806000;
  --syntax-string: #32643c;
  --syntax-value: #80502b;
  --syntax-builtin: #315e87;
  --select-arrow: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 16 16' fill='none'%3E%3Cpath d='m4 6 4 4 4-4' stroke='%236c665b' stroke-width='1.5' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E");
}

/* Follow the system theme while retaining the playground's gold accents. */
@media (prefers-color-scheme: dark) {
  :root {
    --page: #181713;
    --paper: #24221f;
    --ink: #f3efe6;
    --muted: #bcb5a8;
    --line: #474239;
    --accent: #f4cd62;
    --primary: #f4c430;
    --primary-hover: #ffda63;
    --wash: #342d1c;
    --surface-hover: #302c25;
    --gutter: #201e1a;
    --selection: #66521d;
    --control-border: #8f8473;
    --error: #ff9b91;
    --syntax-keyword: #f4cd62;
    --syntax-string: #a6cc9c;
    --syntax-value: #e6b28d;
    --syntax-builtin: #9fc8e6;
    --select-arrow: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 16 16' fill='none'%3E%3Cpath d='m4 6 4 4 4-4' stroke='%23bcb5a8' stroke-width='1.5' stroke-linecap='round' stroke-linejoin='round'/%3E%3C/svg%3E");
  }
}

* {
  box-sizing: border-box;
}

[hidden] {
  display: none !important;
}

body {
  margin: 0;
  background: var(--page);
  color: var(--ink);
  font:
    16px/1.55 system-ui,
    -apple-system,
    BlinkMacSystemFont,
    'Segoe UI',
    sans-serif;
}

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

a {
  color: var(--accent);
  text-underline-offset: 4px;
}

button,
select,
textarea {
  font: inherit;
}

button,
select {
  min-height: 44px;
  border: 1px solid var(--control-border);
  border-radius: 6px;
  background: var(--paper);
  color: var(--ink);
}

button {
  padding: 8px 16px;
  font-weight: 600;
  cursor: pointer;
}

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

button:disabled {
  opacity: 0.5;
  cursor: default;
}

:focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 3px;
}

svg {
  width: 16px;
  height: 16px;
  flex: none;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.5;
  stroke-linecap: round;
  stroke-linejoin: round;
}

main {
  max-width: 1240px;
  margin: auto;
  padding: 28px 20px 100px;
}

h1,
h2,
h3,
p {
  margin: 0;
}

h1 {
  font-size: 28px;
  line-height: 1.2;
  letter-spacing: -0.025em;
  font-weight: 700;
}

h1 a {
  color: inherit;
  text-decoration: none;
}

h1 a:hover {
  text-decoration: underline;
}

h1 span {
  font-weight: 400;
  color: var(--muted);
}

.site-header {
  display: flex;
  justify-content: space-between;
  gap: 20px;
  align-items: flex-start;
  padding-bottom: 24px;
  border-bottom: 1px solid var(--line);
}

.site-header p {
  margin-top: 10px;
  max-width: 60ch;
  color: var(--muted);
  font-size: 15px;
}

.guide-link {
  display: none;
  align-items: center;
  gap: 8px;
  min-height: 44px;
  white-space: nowrap;
  font-size: 14px;
  font-weight: 600;
}

.example-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  padding: 24px 0;
}

.example-picker {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px;
  width: 100%;
}

.example-picker label {
  width: 100%;
  font-weight: 600;
  font-size: 14px;
}

select {
  appearance: none;
  padding: 8px 40px 8px 12px;
  flex: 1;
  min-width: 0;
  max-width: 100%;
  background-image: var(--select-arrow);
  background-repeat: no-repeat;
  background-position: right 12px center;
  background-size: 16px 16px;
}

.local-note {
  display: none;
  color: var(--muted);
  font-size: 13px;
  white-space: nowrap;
}

.lesson {
  display: grid;
  gap: 20px 40px;
  padding-bottom: 24px;
}

.lesson h2 {
  font-size: 23px;
  line-height: 1.3;
  letter-spacing: -0.02em;
  font-weight: 650;
  margin-bottom: 8px;
}

.lesson-intro p {
  max-width: 64ch;
  color: var(--muted);
  font-size: 15px;
}

.concepts {
  margin: 0;
  display: grid;
  gap: 6px;
  font-size: 14px;
}

.concepts div {
  display: grid;
  grid-template-columns: minmax(100px, 0.85fr) 1.4fr;
  gap: 16px;
}

.concepts dt {
  color: var(--ink);
}

.concepts dd {
  margin: 0;
  color: var(--muted);
}

code,
pre {
  font-family: var(--code-font);
}

.challenge {
  display: flex;
  gap: 8px 16px;
  flex-wrap: wrap;
  background: var(--wash);
  padding: 14px 16px;
  border-radius: 6px;
  font-size: 14px;
}

.challenge strong {
  color: var(--accent);
  white-space: nowrap;
}

.challenge span {
  flex: 1;
  min-width: 200px;
}

.draft-notice {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  padding: 8px 0 16px;
  font-size: 14px;
}

.workspace {
  display: grid;
  gap: 0;
  scroll-margin-top: 16px;
}

.pane {
  min-width: 0;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--paper);
  overflow: hidden;
}

.pane-heading {
  display: flex;
  align-items: center;
  gap: 12px;
  min-height: 54px;
  padding: 4px 16px;
  border-bottom: 1px solid var(--line);
}

.pane-heading label,
.pane-heading h2 {
  font-size: 14px;
  font-weight: 650;
}

#draft-status,
#status {
  margin-left: auto;
  color: var(--muted);
  font-size: 12px;
}

.text-button {
  padding: 6px 8px;
  border: 0;
  background: transparent;
  color: var(--accent);
  font-size: 13px;
  text-decoration: underline;
  text-underline-offset: 3px;
}

.code-editor {
  display: grid;
  grid-template-columns: 40px minmax(0, 1fr);
  height: 330px;
}

#line-numbers {
  margin: 0;
  padding: 16px 8px 16px 0;
  text-align: right;
  color: var(--muted);
  background: var(--gutter);
  overflow: hidden;
  user-select: none;
  font: 16px/26px var(--code-font);
}

textarea {
  width: 100%;
  height: 100%;
  min-width: 0;
  resize: none;
  border: 0;
  border-radius: 0;
  background: var(--paper);
  color: var(--ink);
  padding: 16px 12px;
  caret-color: var(--accent);
  font: 16px/26px var(--code-font);
  tab-size: 4;
  white-space: pre;
  overflow: auto;
  scrollbar-color: var(--line) var(--paper);
}

textarea:focus-visible {
  outline-offset: -3px;
}

textarea[aria-invalid='true'] {
  box-shadow: inset 0 0 0 1px var(--error);
}

code-input#source {
  margin: 0;
  width: 100%;
  height: 100%;
  min-width: 0;
  min-height: 0;
  --padding-top: 16px;
  --padding-bottom: 16px;
  --padding-left: 12px;
  --padding-right: 12px;
  background: var(--paper);
  color: var(--ink);
  caret-color: var(--accent);
  font: 16px/26px var(--code-font);
  tab-size: 4;
  scrollbar-color: var(--line) var(--paper);
  outline-offset: -3px;
}

code-input#source:has(textarea:focus-visible) {
  outline: 2px solid var(--accent);
}

code-input#source[aria-invalid='true'] {
  box-shadow: inset 0 0 0 1px var(--error);
}

/* The component scrolls both layers together; only the overlay shows text. */
code-input#source textarea {
  width: auto;
  height: auto;
}

code-input#source textarea:not([data-code-input-fallback])::selection {
  background: var(--selection);
  color: transparent;
}

code-input#source pre,
code-input#source code {
  background: transparent;
  color: var(--ink);
}

code-input#source .token.keyword,
code-input#source .token.operator {
  color: var(--syntax-keyword);
}

code-input#source .token.string {
  color: var(--syntax-string);
}

code-input#source .token.number,
code-input#source .token.boolean {
  color: var(--syntax-value);
}

code-input#source .token.builtin {
  color: var(--syntax-builtin);
}

/* A failed optional dependency leaves an ordinary, labeled editor. */
code-input#source:has(textarea[data-code-input-fallback])::after {
  content: none;
}

code-input#source textarea[data-code-input-fallback] {
  min-height: calc(100% - 32px);
  height: calc(100% - 32px);
  padding-bottom: 16px !important;
}

.pane-footnote {
  padding: 10px 16px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 12px;
}

.output-pane {
  display: flex;
  flex-direction: column;
}

.result {
  padding: 20px;
  min-height: 280px;
  flex: 1;
  overflow: auto;
  scrollbar-color: var(--line) var(--paper);
}

pre {
  font-size: 14px;
  line-height: 1.7;
  white-space: pre-wrap;
  overflow-wrap: anywhere;
}

#output {
  margin: 0;
  font-size: 16px;
}

#output:empty {
  display: none;
}

#placeholder {
  color: var(--muted);
  font-size: 14px;
  max-width: 34ch;
}

#placeholder p + p {
  margin-top: 8px;
}

.empty-title {
  color: var(--ink);
  font-weight: 600;
  font-size: 16px;
}

.error-box {
  color: var(--error);
  font-size: 14px;
}

#output:not(:empty) + .error-box {
  margin-top: 20px;
  border-top: 1px solid var(--line);
  padding-top: 16px;
}

.error-box details {
  margin-top: 8px;
  color: var(--muted);
}

.error-box pre {
  font-size: 12px;
  margin: 8px 0 0;
}

.error-box .text-button {
  color: var(--error);
  padding-left: 0;
}

summary {
  cursor: pointer;
  min-height: 44px;
  align-content: center;
}

.expected {
  border-top: 1px solid var(--line);
  padding: 0 16px;
  color: var(--muted);
  font-size: 12px;
}

.expected pre {
  color: var(--ink);
  margin: 0 0 16px;
}

.next-lesson {
  margin-top: 24px;
  color: var(--accent);
  font-size: 14px;
}

.runbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  position: sticky;
  bottom: 0;
  padding: 12px 0;
  background: var(--page);
  z-index: 2;
}

.actions {
  display: flex;
  gap: 8px;
}

#run {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  background: var(--primary);
  color: var(--primary-ink);
  border-color: var(--accent);
}

#run:hover:not(:disabled) {
  background: var(--primary-hover);
}

#run svg {
  fill: currentColor;
  stroke: none;
}

.run-hint {
  display: none;
  font-size: 12px;
  color: var(--muted);
}

kbd {
  font-family: inherit;
}

.view-switch {
  display: flex;
  gap: 4px;
}

.view-switch button {
  border: 0;
  padding: 8px 10px;
  background: transparent;
  color: var(--muted);
  font-size: 14px;
}

.view-switch button[aria-pressed='true'] {
  background: var(--primary);
  color: var(--primary-ink);
  box-shadow: inset 0 0 0 1px var(--accent);
}

body.enhanced .workspace[data-view='source'] .output-pane,
body.enhanced .workspace[data-view='output'] .source-pane {
  display: none;
}

body.enhanced .runbar {
  position: fixed;
  left: 0;
  right: 0;
  bottom: 0;
  padding: 10px 16px max(10px, env(safe-area-inset-bottom));
  border-top: 1px solid var(--line);
  background: var(--paper);
}

.syntax-guide {
  margin-top: 24px;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  padding: 8px 0;
  scroll-margin-top: 16px;
}

.syntax-guide > summary {
  font-size: 17px;
  font-weight: 600;
  padding: 8px 0;
}

.syntax-guide > summary span {
  display: none;
  font-weight: 400;
  color: var(--muted);
  font-size: 14px;
  margin-left: 12px;
}

.reference-grid {
  display: grid;
  gap: 28px;
  padding: 20px 0;
}

.reference-grid h3 {
  font-size: 15px;
  font-weight: 650;
}

.reference-grid pre {
  margin: 12px 0;
  color: var(--ink);
  font-size: 13px;
}

.reference-grid p,
.reference-note {
  font-size: 14px;
  color: var(--muted);
}

.reference-note {
  padding-bottom: 20px;
  max-width: 80ch;
}

footer {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 24px;
  justify-content: space-between;
  padding-top: 24px;
  font-size: 12px;
  color: var(--muted);
}

@media (min-width: 760px) {
  main {
    padding: 36px 32px;
  }

  .site-header {
    align-items: center;
  }

  .guide-link {
    display: flex;
  }

  .example-picker {
    width: auto;
  }

  .example-picker label {
    width: auto;
    margin-right: 6px;
  }

  select {
    flex: initial;
  }

  .lesson {
    grid-template-columns: 1.3fr 1fr;
  }

  .challenge {
    grid-column: 1/-1;
  }

  .workspace {
    grid-template-columns: minmax(0, 3fr) minmax(0, 2fr);
    gap: 0 20px;
  }

  body.enhanced .workspace[data-view] .source-pane {
    display: block;
  }

  body.enhanced .workspace[data-view] .output-pane {
    display: flex;
  }

  .code-editor {
    height: 350px;
  }

  .view-switch {
    display: none;
  }

  body.enhanced .runbar {
    grid-column: 1/-1;
    position: static;
    border: 0;
    padding: 0 0 12px;
    background: transparent;
  }

  .run-hint {
    display: block;
  }

  .syntax-guide {
    margin-top: 28px;
  }

  .syntax-guide > summary span {
    display: inline;
  }

  .reference-grid {
    grid-template-columns: 1fr 1fr;
    gap: 28px 48px;
  }
}

@media (min-width: 1050px) {
  .local-note {
    display: block;
  }
}

@media (max-width: 359px) {
  main {
    padding-inline: 14px;
  }

  .actions {
    gap: 4px;
  }

  .actions button {
    padding-inline: 10px;
  }

  #draft-status {
    max-width: 90px;
  }
}

@media (forced-colors: active) {
  select {
    appearance: auto;
    background-image: none;
  }

  #run {
    border: 1px solid ButtonText;
  }

  .view-switch button[aria-pressed='true'] {
    outline: 1px solid ButtonText;
  }
}