* { box-sizing: border-box; }

:root {
  color-scheme: dark;
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  --background: #070a12;
  --panel: rgba(12, 17, 31, 0.9);
  --panel-strong: #11192c;
  --line: #2d3b5e;
  --line-strong: #5570ad;
  --text: #f2f5ff;
  --muted: #aab6d4;
  --blue: #81a7ff;
  --cyan: #70d8ff;
  --gold: #ffc968;
  --danger: #ff9aab;
  --checkers-light: #c7b48d;
  --checkers-dark: #403a49;
  --checkers-dark-active: #62547a;
  --checkers-black: #12141b;
  --checkers-red: #b53b48;
}

body {
  margin: 0;
  min-height: 100vh;
  background:
    radial-gradient(circle at 16% 0%, rgba(57, 91, 166, 0.3), transparent 34rem),
    radial-gradient(circle at 86% 18%, rgba(57, 145, 172, 0.18), transparent 28rem),
    linear-gradient(180deg, #0b1020 0%, var(--background) 70%);
  color: var(--text);
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  opacity: 0.28;
  background-image:
    linear-gradient(rgba(255,255,255,.025) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255,255,255,.025) 1px, transparent 1px);
  background-size: 28px 28px;
  mask-image: linear-gradient(to bottom, black, transparent 78%);
}

button, input { font: inherit; }
button { color: inherit; }

.shell {
  width: min(1040px, calc(100% - 28px));
  margin: 0 auto;
  padding: 48px 0 64px;
}

.hero { margin-bottom: 26px; }
.eyebrow, .section-label {
  margin: 0 0 8px;
  letter-spacing: .2em;
  font-size: .72rem;
  font-weight: 800;
  color: #92a8df;
}

h1, h2, p { text-wrap: pretty; }
h1 {
  margin: 0;
  font-size: clamp(2.7rem, 9vw, 5.8rem);
  line-height: .9;
  letter-spacing: -.055em;
}
h2 { margin: 0; font-size: clamp(1.35rem, 4vw, 2rem); }
.hero-copy { max-width: 760px; margin: 18px 0 0; color: var(--muted); line-height: 1.65; }
.muted { color: var(--muted); }

.panel {
  padding: clamp(18px, 4vw, 30px);
  border: 1px solid var(--line);
  border-radius: 24px;
  background: var(--panel);
  box-shadow: 0 30px 90px rgba(0, 0, 0, .38);
  backdrop-filter: blur(16px);
}

.error-banner {
  margin: 0 0 16px;
  padding: 13px 16px;
  border: 1px solid rgba(255, 154, 171, .45);
  border-radius: 14px;
  background: rgba(112, 26, 45, .34);
  color: #ffd9df;
}

.section-heading { max-width: 660px; }
.section-heading .muted { margin: 10px 0 0; }

.game-grid, .mode-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
}
.game-grid { margin-top: 22px; }
.mode-grid { margin-top: 14px; }

.game-card, .mode-card {
  display: flex;
  align-items: flex-start;
  gap: 14px;
  padding: 18px;
  text-align: left;
  border: 1px solid var(--line);
  border-radius: 18px;
  background: linear-gradient(145deg, rgba(27, 39, 67, .92), rgba(15, 22, 39, .92));
  cursor: pointer;
  transition: transform .15s ease, border-color .15s ease, background .15s ease, box-shadow .15s ease;
}
.game-card { min-height: 108px; }
.mode-card { min-height: 126px; }
.game-card:hover:not(:disabled), .game-card:focus-visible,
.mode-card:hover:not(:disabled), .mode-card:focus-visible {
  transform: translateY(-2px);
  border-color: var(--line-strong);
  background: linear-gradient(145deg, rgba(34, 51, 88, .96), rgba(18, 28, 49, .96));
}
.game-card.is-selected {
  border-color: var(--cyan);
  background: linear-gradient(145deg, rgba(34, 83, 113, .82), rgba(18, 34, 55, .96));
  box-shadow: inset 0 0 0 1px rgba(112, 216, 255, .2), 0 12px 32px rgba(19, 99, 129, .16);
}
.game-card:disabled, .mode-card:disabled { cursor: progress; opacity: .65; }
.game-card strong, .game-card small, .mode-card strong, .mode-card small { display: block; }
.game-card strong, .mode-card strong { margin-bottom: 7px; font-size: 1.08rem; }
.game-card small, .mode-card small { color: var(--muted); line-height: 1.45; }

.game-glyph, .mode-icon {
  display: grid;
  place-items: center;
  flex: 0 0 44px;
  width: 44px;
  height: 44px;
  border: 1px solid rgba(129, 167, 255, .48);
  border-radius: 13px;
  background: rgba(64, 98, 175, .22);
  color: #dce6ff;
  font-weight: 900;
}
.game-glyph.checkers-glyph {
  border-color: rgba(255, 201, 104, .48);
  background: rgba(143, 75, 74, .26);
  color: #ffd5c9;
  font-size: 1.45rem;
}
.mode-icon.duo { color: #d9f7ff; border-color: rgba(112, 216, 255, .45); background: rgba(40, 125, 155, .2); }

.match-header, .status, .actions, .invite-controls {
  display: flex;
  align-items: center;
}
.match-header { justify-content: space-between; gap: 18px; }
.revision {
  padding: 7px 10px;
  border: 1px solid var(--line);
  border-radius: 999px;
  color: var(--muted);
  font-size: .82rem;
  white-space: nowrap;
}
.status {
  min-height: 46px;
  margin: 18px 0;
  padding: 11px 14px;
  border-radius: 13px;
  background: rgba(54, 79, 133, .23);
  color: #dce6ff;
  font-weight: 750;
}

.game-layout {
  display: grid;
  grid-template-columns: minmax(180px, 230px) minmax(0, 1fr);
  gap: clamp(18px, 4vw, 34px);
  align-items: center;
}
.players { display: grid; gap: 10px; }
.player-card {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px;
  border: 1px solid var(--line);
  border-radius: 15px;
  background: rgba(11, 17, 30, .7);
  transition: border-color .15s ease, background .15s ease, transform .15s ease;
}
.player-card.is-active {
  border-color: var(--blue);
  background: rgba(44, 70, 129, .28);
  transform: translateX(3px);
}
.player-card.is-you strong::after { content: " · You"; color: var(--cyan); font-size: .74rem; font-weight: 700; }
.player-card small, .match-meta dt { display: block; color: var(--muted); font-size: .72rem; }
.player-card strong { display: block; margin-top: 2px; }
.mark-badge {
  display: grid;
  place-items: center;
  width: 38px;
  height: 38px;
  border-radius: 11px;
  font-weight: 950;
}
.mark-badge.x { color: #dce6ff; background: rgba(87, 123, 213, .3); }
.mark-badge.o { color: #ffe8b8; background: rgba(190, 126, 38, .25); }
.mark-badge.black { color: #f2f2f5; background: #161923; border: 1px solid #4d5365; }
.mark-badge.red { color: #fff0ed; background: #8f2f3a; border: 1px solid #d66a74; }

.match-meta { margin: 8px 0 0; padding: 13px; border-top: 1px solid var(--line); }
.match-meta div + div { margin-top: 10px; }
.match-meta dd { margin: 3px 0 0; overflow-wrap: anywhere; color: #d5def6; font-size: .78rem; }

.board-wrap {
  width: min(100%, 620px);
  margin: 0 auto;
  padding: clamp(8px, 2vw, 14px);
  border: 1px solid var(--line);
  border-radius: 22px;
  background: linear-gradient(145deg, rgba(17, 26, 46, .95), rgba(8, 13, 24, .95));
}
.board {
  display: grid;
  width: 100%;
  overflow: hidden;
}
.board-tic-tac-toe {
  grid-template-columns: repeat(3, 1fr);
  gap: clamp(6px, 1.4vw, 10px);
}
.board-checkers {
  grid-template-columns: repeat(8, 1fr);
  gap: 0;
  border: clamp(4px, 1vw, 8px) solid #241f28;
  border-radius: 10px;
  background: #241f28;
  box-shadow: 0 16px 40px rgba(0, 0, 0, .34);
}
.cell {
  position: relative;
  aspect-ratio: 1;
  color: var(--text);
  line-height: 1;
}

.tic-cell {
  border: 1px solid #344568;
  border-radius: clamp(11px, 2vw, 17px);
  background: linear-gradient(145deg, #151f35, #0e1525);
  font-size: clamp(2.5rem, 10vw, 5.5rem);
  font-weight: 900;
  cursor: pointer;
  box-shadow: inset 0 1px rgba(255,255,255,.035);
  transition: transform .12s ease, border-color .12s ease, background .12s ease, box-shadow .12s ease;
}
.tic-cell:hover:enabled, .tic-cell:focus-visible {
  transform: translateY(-2px);
  border-color: var(--blue);
  background: linear-gradient(145deg, #1c2b4b, #121d33);
  box-shadow: 0 10px 26px rgba(31, 73, 155, .22);
}
.tic-cell:disabled { cursor: default; }
.tic-cell:disabled:not([data-mark=""]) { opacity: .62; }
.tic-cell.mark-x { color: #a9c1ff; text-shadow: 0 0 24px rgba(91, 134, 241, .34); }
.tic-cell.mark-o { color: var(--gold); text-shadow: 0 0 24px rgba(255, 180, 62, .24); }

.checkers-cell {
  display: grid;
  place-items: center;
  min-width: 0;
  padding: 7%;
  border: 0;
  border-radius: 0;
  cursor: default;
  transition: filter .12s ease, box-shadow .12s ease;
}
.checkers-cell.light-square { background: var(--checkers-light); }
.checkers-cell.dark-square { background: var(--checkers-dark); }
.checkers-cell.dark-square:enabled { cursor: pointer; }
.checkers-cell.selectable-piece {
  box-shadow: inset 0 0 0 clamp(2px, .45vw, 4px) rgba(112, 216, 255, .72);
}
.checkers-cell.legal-destination {
  background: var(--checkers-dark-active);
  box-shadow: inset 0 0 0 clamp(2px, .45vw, 4px) rgba(255, 214, 128, .9);
}
.checkers-cell.legal-destination::after {
  content: "";
  width: 28%;
  aspect-ratio: 1;
  border-radius: 50%;
  background: rgba(255, 226, 160, .72);
  box-shadow: 0 0 16px rgba(255, 210, 102, .5);
}
.checkers-cell.selected-piece,
.checkers-cell.selected-path {
  box-shadow: inset 0 0 0 clamp(3px, .55vw, 5px) rgba(255, 201, 104, .95);
}
.checkers-cell:focus-visible {
  z-index: 2;
  outline: 3px solid var(--cyan);
  outline-offset: -3px;
}
.checkers-piece {
  display: grid;
  place-items: center;
  width: 80%;
  aspect-ratio: 1;
  border-radius: 50%;
  font-size: clamp(.55rem, 2.3vw, 1.15rem);
  font-weight: 950;
  pointer-events: none;
  box-shadow:
    inset 0 4px 7px rgba(255,255,255,.16),
    inset 0 -5px 8px rgba(0,0,0,.38),
    0 5px 8px rgba(0,0,0,.38);
}
.piece-black {
  border: 2px solid #555c6b;
  background: radial-gradient(circle at 36% 28%, #3d424e, var(--checkers-black) 68%);
  color: #f3e4aa;
}
.piece-red {
  border: 2px solid #ed8790;
  background: radial-gradient(circle at 36% 28%, #de6470, var(--checkers-red) 68%);
  color: #fff0bd;
}
.checkers-piece.is-king {
  border-width: 3px;
  box-shadow:
    inset 0 0 0 3px rgba(255, 215, 118, .62),
    inset 0 4px 7px rgba(255,255,255,.16),
    inset 0 -5px 8px rgba(0,0,0,.38),
    0 5px 8px rgba(0,0,0,.38);
}
.placeholder-board { opacity: .54; }
.board-help {
  min-height: 1.35em;
  margin: 11px 4px 0;
  color: var(--muted);
  font-size: .82rem;
  text-align: center;
}

.invite-panel {
  display: grid;
  gap: 12px;
  margin-top: 22px;
  padding: 16px;
  border: 1px solid rgba(112, 216, 255, .3);
  border-radius: 16px;
  background: rgba(34, 101, 126, .14);
}
.invite-panel p { margin: 5px 0 0; color: var(--muted); font-size: .86rem; line-height: 1.45; }
.invite-controls { gap: 10px; }
.invite-controls input {
  min-width: 0;
  flex: 1;
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: 11px;
  background: #080d18;
  color: #cbd8fa;
}
.actions { justify-content: flex-end; margin-top: 18px; }
.secondary-button {
  padding: 10px 14px;
  border: 1px solid var(--line-strong);
  border-radius: 11px;
  background: rgba(31, 45, 76, .78);
  color: #e5ebff;
  font-weight: 750;
  cursor: pointer;
}
.secondary-button:hover:not(:disabled), .secondary-button:focus-visible { background: rgba(48, 68, 111, .88); }
.secondary-button:disabled { opacity: .55; cursor: progress; }

.diagnostics { margin-top: 16px; color: var(--muted); font-size: .82rem; }
.diagnostics summary { cursor: pointer; }
.details {
  max-height: 210px;
  margin: 10px 0 0;
  padding: 13px;
  overflow: auto;
  border-radius: 11px;
  background: #070b13;
  color: #9fb0d9;
  font-size: .76rem;
}

[hidden] { display: none !important; }

@media (max-width: 760px) {
  .shell { padding: 28px 0 46px; }
  .game-layout { grid-template-columns: 1fr; }
  .players { grid-template-columns: repeat(2, minmax(0, 1fr)); order: 2; }
  .match-meta { grid-column: 1 / -1; display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 12px; }
  .match-meta div + div { margin-top: 0; }
  .board-wrap { order: 1; }
}

@media (max-width: 600px) {
  .shell { width: min(100% - 18px, 1040px); padding-top: 20px; }
  .panel { border-radius: 18px; }
  .game-grid, .mode-grid { grid-template-columns: 1fr; }
  .game-card, .mode-card { min-height: 102px; }
  .match-header { align-items: flex-start; }
  .invite-controls { align-items: stretch; flex-direction: column; }
  .invite-controls input, .invite-controls button { width: 100%; }
  .checkers-cell { padding: 5%; }
}

@media (max-width: 420px) {
  .shell { width: min(100% - 12px, 1040px); }
  .panel { padding: 14px; }
  .players { grid-template-columns: 1fr; }
  .match-meta { grid-template-columns: 1fr 1fr; }
  .board-wrap { padding: 6px; border-radius: 14px; }
  .board-checkers { border-width: 4px; }
  .status { font-size: .9rem; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { scroll-behavior: auto !important; transition: none !important; }
}