:root {
  color-scheme: dark;
  --space: #0b0d17;
  --panel: #171a2b;
  --empty: #232741;
  --text: #eef0fa;
  --muted: #a4a9c6;
  --accent: #ffd75f;
  --slide-ms: 200ms;
  --ending-delay: 300ms; /* Lets the last move finish first. */
  --ending-fade: 700ms;

  /* Tile colors follow the terminal version's palette. */
  --tile-1: #8a8a8a; --ink-1: #000;
  --tile-2: #875f00; --ink-2: #fff8e1;
  --tile-3: #007699; --ink-3: #fff;
  --tile-4: #bcbcbc; --ink-4: #000;
  --tile-5: #afd7ff; --ink-5: #000;
  --tile-6: #5f5faf; --ink-6: #fff;
  --tile-7: #ff5f00; --ink-7: #000;
  --tile-8: #5f0000; --ink-8: #fff;
  --tile-9: #8f45b8; --ink-9: #fff;
  --tile-10: #ff87ff; --ink-10: #000;
  --tile-11: #fff; --ink-11: #000;
}

/* The plants theme only swaps the tile colors. Each background is light or
   dark enough that its glyph stands out, and the ink is readable on it. */
:root[data-theme="plants"] {
  --tile-1: #d0d0d0; --ink-1: #000;
  --tile-2: #ffffaf; --ink-2: #000;
  --tile-3: #87d7ff; --ink-3: #000;
  --tile-4: #af5f00; --ink-4: #fff;
  --tile-5: #d7ffd7; --ink-5: #000;
  --tile-6: #005faf; --ink-6: #fff;
  --tile-7: #5f005f; --ink-7: #fff;
  --tile-8: #d75f5f; --ink-8: #000;
  --tile-9: #ffd7af; --ink-9: #000;
  --tile-10: #d7d7ff; --ink-10: #000;
  --tile-11: #ffd700; --ink-11: #000;
}

* {
  box-sizing: border-box;
}

html {
  background: var(--space);
}

body {
  margin: 0;
  min-height: 100dvh;
  color: var(--text);
  background: var(--space);
  font: 16px/1.4 system-ui, -apple-system, "Segoe UI", sans-serif;
  overscroll-behavior: none;
}

.app {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 14px;
  width: min(100%, 560px);
  margin-inline: auto;
  padding: max(14px, env(safe-area-inset-top)) max(16px, env(safe-area-inset-right)) max(16px, env(safe-area-inset-bottom)) max(16px, env(safe-area-inset-left));
}

.top {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px 12px;
}

h1 {
  flex: 1 1 auto;
  margin: 0;
  color: var(--accent);
  font-size: 1.6rem;
  letter-spacing: 0.04em;
}

.stats {
  display: flex;
  gap: 6px;
}

.stat {
  display: grid;
  min-width: 68px;
  padding: 3px 10px;
  border-radius: 8px;
  background: var(--panel);
  text-align: center;
}

.stat span {
  color: var(--muted);
  font-size: 0.7rem;
  text-transform: uppercase;
}

.stat output {
  font-weight: 700;
  font-variant-numeric: tabular-nums;
}

button {
  min-height: 44px;
  padding: 0 14px;
  border: 0;
  border-radius: 8px;
  background: var(--accent);
  color: #1a1400;
  font: inherit;
  font-weight: 700;
  cursor: pointer;
}

button:hover {
  filter: brightness(1.08);
}

button:focus-visible {
  outline: 3px solid var(--text);
  outline-offset: 2px;
}

/* Every tile is a square because the board is square and divides evenly. */
.board {
  position: relative;
  container-type: inline-size;
  aspect-ratio: 1;
  width: min(100%, calc(100dvh - 230px));
  min-width: min(100%, 280px);
  margin-inline: auto;
  border-radius: 12px;
  background: var(--panel);
  touch-action: none;
  user-select: none;
  -webkit-user-select: none;
}

.layer {
  --gap: 2.2cqw;
  position: absolute;
  inset: var(--gap);
}

.cells {
  display: grid;
  grid-template: repeat(4, 1fr) / repeat(4, 1fr);
  gap: var(--gap);
}

.cells div {
  border-radius: 6px;
  background: var(--empty);
}

.tile {
  position: absolute;
  display: grid;
  grid-template-rows: minmax(0, 1fr) auto;
  justify-items: center;
  /* Both sides use the same formula on a square layer, so content can't stretch a tile. */
  width: calc((100% - 3 * var(--gap)) / 4);
  height: calc((100% - 3 * var(--gap)) / 4);
  overflow: hidden;
  padding-block: 4% 7%;
  border-radius: 6px;
  background: var(--tile);
  color: var(--ink);
  transform: translate(
    calc(var(--c) * (100% + var(--gap))),
    calc(var(--r) * (100% + var(--gap)))
  );
  transition: transform var(--slide-ms) cubic-bezier(0.33, 0, 0.2, 1);
}

.tile .rank {
  position: absolute;
  top: 4%;
  left: 8%;
  font-size: clamp(9px, 2.2cqw, 13px);
  font-weight: 700;
  opacity: 0.8;
}

.tile .glyph {
  align-self: center;
  font-size: 8.5cqw;
  line-height: 1;
}

.tile .name {
  font-size: clamp(10px, 2.7cqw, 15px);
  font-weight: 700;
  line-height: 1.1;
  white-space: nowrap;
}

.tile.spawn {
  animation: spawn 250ms ease-in-out;
}

@keyframes spawn {
  from { opacity: 0; }
}

.overlay {
  position: absolute;
  inset: 0;
  z-index: 2;
  display: grid;
  place-content: center;
  justify-items: center;
  gap: 10px;
  padding: 16px;
  border-radius: 12px;
  background: #0b0d1740;
  text-align: center;
  animation: ending-in var(--ending-fade) ease-in-out var(--ending-delay) both;
}

.overlay[hidden] {
  display: none;
}

/* A card keeps the message readable while the board stays visible around it. */
.overlay-card {
  display: grid;
  justify-items: center;
  gap: 10px;
  padding: 18px 20px;
  border-radius: 12px;
  background: #0b0d17eb;
}

.board.game-over #tiles {
  filter: grayscale(0.6) brightness(0.85);
  transition: filter var(--ending-fade) ease-in-out var(--ending-delay);
}

@keyframes ending-in {
  from { opacity: 0; }
}

.overlay h2 {
  margin: 0;
  color: var(--accent);
  font-size: clamp(1.3rem, 6cqw, 2rem);
}

.overlay p {
  margin: 0;
}

.overlay-actions {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 8px;
}

#keep-going[hidden] {
  display: none;
}

.theme {
  display: grid;
  gap: 4px;
  justify-items: center;
}

.theme-row {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 4px 10px;
}

.theme-label {
  color: var(--muted);
  font-size: 0.8rem;
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

/* 16px text stops phones zooming in when the control is focused. */
.theme-select {
  min-width: 130px;
  min-height: 44px;
  padding-inline: 10px;
  border: 1px solid var(--muted);
  border-radius: 8px;
  background: var(--panel);
  color: var(--text);
  font: inherit;
  font-size: 16px;
  cursor: pointer;
}

.theme-select:focus-visible {
  outline: 3px solid var(--text);
  outline-offset: 2px;
}

.theme-select:disabled {
  border-color: transparent;
  color: var(--muted);
  cursor: default;
}

.theme-note {
  margin: 0;
  color: var(--muted);
  font-size: 0.8rem;
  text-align: center;
}

.help {
  margin: 0;
  color: var(--muted);
  font-size: 0.9rem;
  text-align: center;
}

kbd {
  padding: 0 5px;
  border: 1px solid var(--muted);
  border-radius: 4px;
  font: inherit;
}

.tiers h2 {
  margin: 0 0 8px;
  color: var(--muted);
  font-size: 0.8rem;
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.tiers ol {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(140px, 1fr));
  gap: 4px 12px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.tiers li {
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--muted);
  font-size: 0.92rem;
}

.tiers li .number {
  min-width: 2ch;
  font-variant-numeric: tabular-nums;
  text-align: right;
}

.tiers li.reached {
  color: var(--text);
}

.tiers li.highest {
  color: var(--accent);
  font-weight: 700;
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

.fatal {
  max-width: 40ch;
  margin: 30px auto;
  padding-inline: 16px;
  text-align: center;
}

/* Phones: keep the title, scores and button on one line where they fit. */
@media (max-width: 430px) {
  .top {
    gap: 8px;
  }

  h1 {
    font-size: 1.25rem;
    letter-spacing: 0;
  }

  .stat {
    min-width: 54px;
    padding-inline: 6px;
  }

  .top button {
    padding-inline: 10px;
    font-size: 0.9rem;
  }
}

.help .touch-help {
  display: none;
}

/* Touch screens have no arrow keys to mention. */
@media (pointer: coarse) {
  .help .key-help {
    display: none;
  }

  .help .touch-help {
    display: inline;
  }
}

/* Wide screens: the tile list sits beside the board. */
@media (min-width: 800px) {
  .app {
    grid-template-columns: minmax(0, 560px) 190px;
    grid-template-areas:
      "top top"
      "board tiers"
      "theme tiers"
      "help help";
    justify-content: center;
    width: min(100%, 800px);
    column-gap: 28px;
  }

  .top { grid-area: top; }
  .board { grid-area: board; }
  .theme { grid-area: theme; }
  .help { grid-area: help; }
  .tiers { grid-area: tiers; }

  .tiers ol {
    grid-template-columns: 1fr;
  }
}

@media (prefers-reduced-motion: reduce) {
  .tile {
    transition: none;
  }

  .tile.spawn,
  .overlay {
    animation: none;
  }

  .board.game-over #tiles {
    transition: none;
  }
}