:root {
  color-scheme: dark;
  --bg: #090d13;
  --surface: #101720;
  --surface-raised: #151e29;
  --surface-soft: #0d131b;
  --border: #263241;
  --border-bright: #34445a;
  --text: #ecf2f8;
  --muted: #8fa0b4;
  --subtle: #65768a;
  --accent: #7ee787;
  --accent-strong: #56d364;
  --accent-soft: rgba(126, 231, 135, 0.12);
  --blue: #79c0ff;
  --blue-soft: rgba(121, 192, 255, 0.12);
  --danger: #ff7b72;
  --warning: #d29922;
  --shadow: 0 20px 60px rgba(0, 0, 0, 0.32);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

* { box-sizing: border-box; }

html, body { min-height: 100%; }

body {
  margin: 0;
  background:
    radial-gradient(circle at 10% -20%, rgba(71, 118, 230, 0.16), transparent 36rem),
    radial-gradient(circle at 90% 0%, rgba(46, 160, 67, 0.09), transparent 30rem),
    var(--bg);
  color: var(--text);
}

button, select, textarea { font: inherit; }
button { color: inherit; }

.skip-link {
  position: fixed;
  top: -4rem;
  left: 1rem;
  z-index: 100;
  padding: 0.7rem 1rem;
  background: var(--text);
  color: var(--bg);
  border-radius: 0.5rem;
}
.skip-link:focus { top: 1rem; }

.topbar {
  height: 4.25rem;
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 1.5rem;
  padding: 0 2rem;
  border-bottom: 1px solid rgba(52, 68, 90, 0.75);
  background: rgba(9, 13, 19, 0.88);
  backdrop-filter: blur(18px);
  position: sticky;
  top: 0;
  z-index: 20;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.75rem;
  width: max-content;
  color: var(--text);
  text-decoration: none;
}
.brand-mark {
  display: grid;
  place-items: center;
  width: 2.25rem;
  aspect-ratio: 1;
  border-radius: 0.65rem;
  background: linear-gradient(145deg, var(--accent), #2ea043);
  color: #07120a;
  font-weight: 900;
  box-shadow: 0 0 24px rgba(126, 231, 135, 0.2);
}
.brand strong, .brand small { display: block; }
.brand strong { font-size: 0.9rem; }
.brand small { margin-top: 0.12rem; color: var(--muted); font-size: 0.7rem; }

.topbar-nav {
  display: flex;
  gap: 0.25rem;
  padding: 0.25rem;
  border: 1px solid var(--border);
  border-radius: 0.7rem;
  background: var(--surface-soft);
}
.topbar-nav a {
  padding: 0.45rem 0.8rem;
  border-radius: 0.48rem;
  color: var(--muted);
  text-decoration: none;
  font-size: 0.8rem;
  font-weight: 700;
}
.topbar-nav a:hover, .topbar-nav a.active { color: var(--text); background: var(--surface-raised); }

.runtime-badge {
  justify-self: end;
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--muted);
  font: 600 0.72rem ui-monospace, SFMono-Regular, Menlo, monospace;
}
.runtime-dot {
  width: 0.5rem;
  aspect-ratio: 1;
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 0 0.25rem var(--accent-soft);
}

.page-shell {
  width: min(1680px, calc(100% - 2.5rem));
  margin: 0 auto;
  padding: 1.75rem 0 2rem;
}

.exercise-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 2rem;
  margin-bottom: 1.25rem;
}
.exercise-copy { max-width: 900px; }
.eyebrow-row { display: flex; align-items: center; gap: 0.65rem; }
.eyebrow {
  color: var(--blue);
  font-size: 0.67rem;
  font-weight: 800;
  letter-spacing: 0.13em;
  text-transform: uppercase;
}
.mode-chip, .status-chip, .result-badge {
  padding: 0.27rem 0.52rem;
  border: 1px solid var(--border);
  border-radius: 999px;
  color: var(--muted);
  background: var(--surface-soft);
  font: 600 0.68rem ui-monospace, SFMono-Regular, Menlo, monospace;
}
.exercise-header h1 {
  margin: 0.5rem 0 0.45rem;
  font-size: clamp(1.55rem, 3vw, 2.3rem);
  letter-spacing: -0.04em;
}
.exercise-header p {
  margin: 0;
  color: var(--muted);
  line-height: 1.55;
  white-space: pre-wrap;
}
.header-actions, .toolbar-actions, .run-actions, .dialog-actions > div {
  display: flex;
  align-items: center;
  gap: 0.55rem;
}

.button, .icon-button {
  border: 1px solid var(--border-bright);
  border-radius: 0.55rem;
  cursor: pointer;
  transition: border-color 140ms ease, background 140ms ease, transform 140ms ease;
}
.button {
  min-height: 2.35rem;
  padding: 0.58rem 0.85rem;
  font-size: 0.78rem;
  font-weight: 750;
}
.button:hover:not(:disabled), .icon-button:hover:not(:disabled) { transform: translateY(-1px); border-color: #52657e; }
.button:disabled, .icon-button:disabled { opacity: 0.42; cursor: not-allowed; }
.button.primary { border-color: #429c4d; background: var(--accent-strong); color: #061008; }
.button.primary:hover:not(:disabled) { background: var(--accent); border-color: var(--accent); }
.button.secondary { background: var(--surface-raised); }
.button.ghost { background: transparent; color: var(--muted); }
.button.danger { color: var(--danger); background: rgba(255, 123, 114, 0.08); border-color: rgba(255, 123, 114, 0.35); }
.icon-button { padding: 0.38rem 0.58rem; background: transparent; color: var(--muted); font-size: 0.7rem; }
.run-icon { margin-right: 0.35rem; font-size: 0.67rem; }
kbd { margin-left: 0.55rem; color: rgba(6, 16, 8, 0.65); font: 700 0.62rem ui-monospace, monospace; }

.workspace {
  display: grid;
  grid-template-columns: minmax(0, 1.65fr) minmax(320px, 0.75fr);
  min-height: 500px;
  border: 1px solid var(--border-bright);
  border-radius: 0.8rem;
  overflow: hidden;
  background: #0d1117;
  box-shadow: var(--shadow);
}
.editor-panel { min-width: 0; display: flex; flex-direction: column; }
.code-panel { border-right: 1px solid var(--border-bright); }
.panel-toolbar {
  min-height: 3.35rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.65rem 0.85rem;
  border-bottom: 1px solid var(--border);
  background: var(--surface);
}
.panel-title { display: flex; align-items: center; gap: 0.65rem; min-width: 0; }
.panel-title strong, .panel-title small { display: block; }
.panel-title strong { font: 700 0.78rem ui-monospace, SFMono-Regular, Menlo, monospace; }
.panel-title small { margin-top: 0.12rem; color: var(--subtle); font-size: 0.66rem; }
.file-dot {
  display: grid;
  place-items: center;
  width: 1.7rem;
  height: 1.7rem;
  border-radius: 0.45rem;
  background: rgba(210, 153, 34, 0.13);
  color: #e3b341;
  font: 800 0.62rem ui-monospace, monospace;
}
.file-dot.json { color: var(--blue); background: var(--blue-soft); }
.case-picker select {
  max-width: 190px;
  height: 2rem;
  padding: 0 1.8rem 0 0.65rem;
  border: 1px solid var(--border);
  border-radius: 0.45rem;
  background: var(--surface-soft);
  color: var(--text);
  font-size: 0.7rem;
}
.editor-host { flex: 1; min-height: 440px; }

.run-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  margin: 0.9rem 0;
  padding: 0.75rem 0.85rem;
  border: 1px solid var(--border);
  border-radius: 0.7rem;
  background: rgba(16, 23, 32, 0.82);
}
.run-meta { display: flex; align-items: center; gap: 0.75rem; color: var(--subtle); font-size: 0.7rem; }
.status-chip.running { color: var(--blue); border-color: rgba(121, 192, 255, 0.35); }
.status-chip.success { color: var(--accent); border-color: rgba(126, 231, 135, 0.35); }
.status-chip.failure { color: var(--danger); border-color: rgba(255, 123, 114, 0.35); }

.result-grid { display: grid; grid-template-columns: minmax(0, 0.8fr) minmax(0, 1.2fr); gap: 0.9rem; }
.result-panel {
  min-width: 0;
  min-height: 255px;
  border: 1px solid var(--border);
  border-radius: 0.75rem;
  overflow: hidden;
  background: var(--surface);
}
.result-heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.78rem 0.9rem;
  border-bottom: 1px solid var(--border);
}
.result-heading h2 { margin: 0.18rem 0 0; font-size: 0.93rem; }
.result-badge.passed { color: var(--accent); border-color: rgba(126, 231, 135, 0.35); }
.result-badge.failed, .result-badge.error { color: var(--danger); border-color: rgba(255, 123, 114, 0.35); }
.output-view, .terminal-view {
  margin: 0;
  padding: 1rem;
  min-height: 160px;
  max-height: 340px;
  overflow: auto;
  color: #d6deeb;
  font: 0.78rem/1.6 ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  white-space: pre-wrap;
  overflow-wrap: anywhere;
}
.result-detail { padding: 0 1rem 0.85rem; color: var(--subtle); font-size: 0.69rem; }
.terminal-view { background: #090d13; }
.terminal-empty { color: var(--subtle); }
.terminal-line { display: grid; grid-template-columns: 4.3rem 1fr; gap: 0.7rem; padding: 0.16rem 0; }
.terminal-line::before { content: attr(data-level); color: var(--subtle); text-transform: uppercase; font-size: 0.6rem; padding-top: 0.14rem; }
.terminal-line.warn::before { color: var(--warning); }
.terminal-line.error::before { color: var(--danger); }
.terminal-line.info::before { color: var(--blue); }
.terminal-line.system::before { color: var(--accent); }

.page-footer {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  padding: 1rem 0 0;
  color: var(--subtle);
  font-size: 0.68rem;
}

.import-dialog {
  width: min(760px, calc(100vw - 2rem));
  padding: 0;
  border: 1px solid var(--border-bright);
  border-radius: 0.85rem;
  background: var(--surface);
  color: var(--text);
  box-shadow: var(--shadow);
}
.import-dialog::backdrop { background: rgba(2, 5, 9, 0.78); backdrop-filter: blur(4px); }
.import-dialog form { padding: 1.25rem; }
.dialog-heading { display: flex; align-items: flex-start; justify-content: space-between; gap: 1rem; }
.dialog-heading h2 { margin: 0.35rem 0 0; font-size: 1.3rem; }
.dialog-close { border: 0; background: transparent; color: var(--muted); cursor: pointer; font-size: 1.6rem; line-height: 1; }
.import-dialog p { color: var(--muted); font-size: 0.82rem; line-height: 1.5; }
.spec-field span { display: block; margin-bottom: 0.4rem; color: var(--muted); font-size: 0.72rem; font-weight: 700; }
.spec-field textarea {
  width: 100%;
  min-height: 290px;
  resize: vertical;
  padding: 0.8rem;
  border: 1px solid var(--border);
  border-radius: 0.55rem;
  background: #090d13;
  color: #d6deeb;
  font: 0.75rem/1.55 ui-monospace, SFMono-Regular, Menlo, monospace;
}
.form-error {
  margin: 0.7rem 0 0;
  padding: 0.7rem;
  border: 1px solid rgba(255, 123, 114, 0.3);
  border-radius: 0.5rem;
  color: #ffa198;
  background: rgba(255, 123, 114, 0.07);
  font: 0.7rem/1.5 ui-monospace, monospace;
  white-space: pre-wrap;
}
.dialog-actions { display: flex; align-items: center; justify-content: space-between; gap: 1rem; margin-top: 1rem; }

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

@media (max-width: 900px) {
  .topbar { grid-template-columns: 1fr auto; padding: 0 1rem; }
  .topbar-nav { display: none; }
  .runtime-badge { grid-column: 2; }
  .page-shell { width: min(100% - 1.25rem, 1680px); }
  .exercise-header { display: block; }
  .header-actions { margin-top: 1rem; }
  .workspace, .result-grid { grid-template-columns: 1fr; }
  .code-panel { border-right: 0; border-bottom: 1px solid var(--border-bright); }
  .editor-host { min-height: 360px; }
  .run-bar, .page-footer { align-items: flex-start; flex-direction: column; }
}

@media (max-width: 560px) {
  .runtime-badge { display: none; }
  .topbar { grid-template-columns: 1fr; }
  .workspace { min-height: auto; }
  .input-toolbar { align-items: flex-start; flex-direction: column; }
  .case-picker, .case-picker select { width: 100%; max-width: none; }
  .run-actions { flex-wrap: wrap; }
  .dialog-actions { align-items: stretch; flex-direction: column-reverse; }
  .dialog-actions > div { justify-content: flex-end; }
}