/* =========================================================================
   Tic-Tac-Toe — elegant static styling
   Design tokens, layout, board, and animations. Light/dark aware.
   ========================================================================= */

:root {
  color-scheme: light dark;

  /* Palette (light) */
  --color-bg: #f8fafc;
  --color-bg-elev: #ffffff;
  --color-text: #0f172a;
  --color-muted: #64748b;
  --color-accent: #2563eb;
  --color-accent-soft: rgba(37, 99, 235, 0.12);
  --color-border: #e2e8f0;
  --color-x: #2563eb; /* crosses */
  --color-o: #e11d48; /* noughts */
  --color-shadow: rgba(15, 23, 42, 0.08);

  /* Type & shape */
  --font-sans: "Segoe UI", system-ui, -apple-system, Roboto, Helvetica, Arial, sans-serif;
  --radius: 16px;
  --radius-sm: 10px;
  --shadow: 0 10px 30px -12px var(--color-shadow);
  --transition: 180ms cubic-bezier(0.4, 0, 0.2, 1);
}

@media (prefers-color-scheme: dark) {
  :root {
    --color-bg: #0b1120;
    --color-bg-elev: #0f172a;
    --color-text: #e2e8f0;
    --color-muted: #94a3b8;
    --color-accent: #60a5fa;
    --color-accent-soft: rgba(96, 165, 250, 0.16);
    --color-border: #1e293b;
    --color-x: #60a5fa;
    --color-o: #fb7185;
    --color-shadow: rgba(0, 0, 0, 0.55);
  }
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  padding: 0;
}

body {
  font-family: var(--font-sans);
  background:
    radial-gradient(1200px 600px at 50% -10%, var(--color-accent-soft), transparent 60%),
    var(--color-bg);
  color: var(--color-text);
  min-height: 100vh;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}

a {
  color: var(--color-accent);
  text-decoration: none;
}
a:hover {
  text-decoration: underline;
}

.app {
  max-width: 640px;
  margin: 0 auto;
  padding: 1.5rem 1.25rem 3rem;
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

/* ------------------------------------------------------------------ Header */
.site-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-bottom: 1.5rem;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.6rem;
  color: var(--color-text);
  font-weight: 700;
  letter-spacing: -0.02em;
}
.brand:hover {
  text-decoration: none;
}
.brand-mark svg {
  display: block;
}
.brand-mark line {
  stroke: var(--color-accent);
  stroke-width: 2.5;
  stroke-linecap: round;
}
.brand-name {
  font-size: 1.15rem;
}

.site-nav {
  display: flex;
  gap: 1.25rem;
  font-weight: 500;
}
.site-nav a {
  color: var(--color-muted);
}
.site-nav a[aria-current="page"] {
  color: var(--color-text);
}

/* ------------------------------------------------------------------ Setup */
.panel {
  background: var(--color-bg-elev);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 1.5rem;
}

.tagline {
  margin: 0 0 1.25rem;
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  text-align: center;
}

.option-group {
  border: 0;
  margin: 0 0 1rem;
  padding: 0;
}
.option-group:last-child {
  margin-bottom: 0;
}
.option-group legend {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-muted);
  margin-bottom: 0.5rem;
  padding: 0;
}

/* Segmented control */
.segmented {
  display: flex;
  gap: 0.4rem;
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  padding: 0.3rem;
}
.seg {
  flex: 1;
  border: 0;
  background: transparent;
  color: var(--color-muted);
  font: inherit;
  font-weight: 600;
  padding: 0.55rem 0.5rem;
  border-radius: 7px;
  cursor: pointer;
  transition: background var(--transition), color var(--transition), transform var(--transition);
}
.seg:hover {
  color: var(--color-text);
}
.seg.is-active {
  background: var(--color-accent);
  color: #fff;
  box-shadow: 0 4px 12px -4px var(--color-accent);
}
.seg:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
}

.hint {
  margin: 0.6rem 0 0;
  font-size: 0.85rem;
  color: var(--color-muted);
  font-style: italic;
  min-height: 1.2em;
}

#difficulty-group[hidden] {
  display: none;
}

/* ------------------------------------------------------------- Scoreboard */
.scoreboard {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.75rem;
  margin: 1.5rem 0 1rem;
}
.score {
  background: var(--color-bg-elev);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  padding: 0.75rem 0.5rem;
  text-align: center;
  transition: border-color var(--transition), box-shadow var(--transition);
}
.score.is-turn {
  border-color: var(--color-accent);
  box-shadow: 0 0 0 3px var(--color-accent-soft);
}
.score-label {
  display: block;
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--color-muted);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.score-value {
  display: block;
  font-size: 1.6rem;
  font-weight: 800;
  letter-spacing: -0.02em;
}
.score-x .score-value {
  color: var(--color-x);
}
.score-o .score-value {
  color: var(--color-o);
}

/* ----------------------------------------------------------------- Status */
.status {
  text-align: center;
  font-size: 1.05rem;
  font-weight: 600;
  min-height: 1.6em;
  margin: 0.5rem 0 1.25rem;
}
.status.is-thinking::after {
  content: "";
  display: inline-block;
  width: 1em;
  text-align: left;
  animation: dots 1.2s steps(4, end) infinite;
}
@keyframes dots {
  0% { content: ""; }
  25% { content: "."; }
  50% { content: ".."; }
  75% { content: "..."; }
}

/* ------------------------------------------------------------------ Board */
.board-wrap {
  position: relative;
  width: min(100%, 420px);
  margin: 0 auto;
  aspect-ratio: 1 / 1;
}

.board {
  position: absolute;
  inset: 0;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-template-rows: repeat(3, 1fr);
  gap: 0.6rem;
}

.cell {
  border: 1px solid var(--color-border);
  background: var(--color-bg-elev);
  border-radius: var(--radius-sm);
  font-size: clamp(2.5rem, 14vw, 5rem);
  font-weight: 800;
  line-height: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  color: var(--color-text);
  box-shadow: var(--shadow);
  transition: transform var(--transition), background var(--transition), box-shadow var(--transition);
  -webkit-user-select: none;
  user-select: none;
}
.cell:hover:not(.is-filled):not(:disabled) {
  transform: translateY(-2px);
  background: var(--color-accent-soft);
}
.cell:focus-visible {
  outline: 3px solid var(--color-accent);
  outline-offset: 2px;
}
.cell:disabled {
  cursor: default;
}
.cell.mark-x {
  color: var(--color-x);
}
.cell.mark-o {
  color: var(--color-o);
}
.cell .glyph {
  display: inline-block;
  animation: pop 220ms cubic-bezier(0.34, 1.56, 0.64, 1);
}
@keyframes pop {
  0% { transform: scale(0.2); opacity: 0; }
  100% { transform: scale(1); opacity: 1; }
}
.cell.is-win {
  background: var(--color-accent-soft);
}

/* Winning line overlay */
.win-line {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
}
.win-line line {
  stroke: var(--color-accent);
  stroke-width: 2.5;
  stroke-linecap: round;
  stroke-dasharray: 160;
  stroke-dashoffset: 160;
}
.win-line.is-shown line {
  animation: draw 420ms ease forwards;
}
@keyframes draw {
  to { stroke-dashoffset: 0; }
}

/* ---------------------------------------------------------------- Controls */
.controls {
  display: flex;
  gap: 0.75rem;
  justify-content: center;
  margin-top: 1.75rem;
}
.btn {
  font: inherit;
  font-weight: 600;
  border: 1px solid var(--color-border);
  background: var(--color-bg-elev);
  color: var(--color-text);
  padding: 0.65rem 1.25rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: transform var(--transition), background var(--transition), border-color var(--transition);
}
.btn:hover {
  transform: translateY(-1px);
  border-color: var(--color-accent);
}
.btn:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
}
.btn-primary {
  background: var(--color-accent);
  color: #fff;
  border-color: transparent;
  box-shadow: 0 6px 16px -6px var(--color-accent);
}

/* ------------------------------------------------------------------ Footer */
.site-footer {
  margin-top: auto;
  padding-top: 2rem;
  text-align: center;
  font-size: 0.85rem;
  color: var(--color-muted);
}

/* --------------------------------------------------------------- Content pages */
.prose {
  background: var(--color-bg-elev);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 2rem;
}
.prose h1 {
  margin-top: 0;
  letter-spacing: -0.02em;
}
.prose h2 {
  margin-top: 2rem;
  letter-spacing: -0.01em;
}
.prose blockquote {
  margin: 1.5rem 0;
  padding: 0.75rem 1.25rem;
  border-left: 3px solid var(--color-accent);
  background: var(--color-accent-soft);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  font-style: italic;
  color: var(--color-text);
}
.prose ul {
  padding-left: 1.25rem;
}
.prose li {
  margin: 0.35rem 0;
}

/* --------------------------------------------------------------- Motion pref */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.001ms !important;
    transition-duration: 0.001ms !important;
  }
}