:root {
  color-scheme: light dark;
  --bg: #f6f7f5;
  --body-gradient-start: rgba(255, 255, 255, 0.7);
  --body-gradient-end: rgba(246, 247, 245, 0.94);
  --panel: #ffffff;
  --panel-soft: #fbfcfd;
  --text: #20242a;
  --muted: #66717f;
  --line: #d8dee4;
  --line-strong: #b7c0ca;
  --tile-bg: #eef4f1;
  --button-bg: #ffffff;
  --button-hover: #f4fbf7;
  --accent: #1f8f62;
  --accent-dark: #166b49;
  --accent-text: #ffffff;
  --accent-soft: #e8f7ef;
  --danger: #b13c3c;
  --shadow: 0 18px 45px rgba(30, 41, 59, 0.09);
  --cover-column: 532px;
  --side-column: 320px;
  --layout-gap: 16px;
  --layout-width: calc(var(--cover-column) + var(--layout-gap) + var(--side-column));
  font-family: Inter, "Segoe UI", "Microsoft YaHei", "PingFang SC", Arial, sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root {
    color-scheme: dark;
    --bg: #0f1211;
    --body-gradient-start: rgba(28, 33, 31, 0.72);
    --body-gradient-end: rgba(15, 18, 17, 0.96);
    --panel: #171c1a;
    --panel-soft: #121715;
    --text: #edf2ef;
    --muted: #a4b0aa;
    --line: #2c3631;
    --line-strong: #47544d;
    --tile-bg: #18221d;
    --button-bg: #121715;
    --button-hover: #19251f;
    --accent: #35c985;
    --accent-dark: #24a76d;
    --accent-text: #ffffff;
    --accent-soft: #163326;
    --danger: #ff817d;
    --shadow: 0 18px 45px rgba(0, 0, 0, 0.36);
  }
}

* {
  box-sizing: border-box;
}

html {
  min-width: 320px;
  background: var(--bg);
}

body {
  min-height: 100vh;
  margin: 0;
  color: var(--text);
  background:
    linear-gradient(180deg, var(--body-gradient-start), var(--body-gradient-end)),
    var(--bg);
}

button {
  color: inherit;
  font: inherit;
}

h1,
h2,
p {
  margin: 0;
}

.app-shell {
  width: min(1180px, calc(100vw - 32px));
  margin: 0 auto;
  padding: 24px 0 32px;
}

.topbar {
  width: min(100%, var(--layout-width));
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
  padding: 14px 0 20px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 14px;
}

.brand-icon {
  width: 52px;
  height: 52px;
  object-fit: contain;
}

h1 {
  font-size: 24px;
  line-height: 1.15;
  letter-spacing: 0;
}

h2 {
  font-size: 20px;
  line-height: 1.2;
  letter-spacing: 0;
}

.workspace {
  display: grid;
  grid-template-columns: minmax(0, var(--cover-column)) minmax(280px, var(--side-column));
  justify-content: center;
  align-items: start;
  gap: var(--layout-gap);
}

.cover-panel,
.controls-panel {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.cover-panel {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 440px;
  padding: 16px;
}

.cover-grid {
  aspect-ratio: 1;
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  width: min(100%, 500px);
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel-soft);
}

.tile {
  position: relative;
  display: flex;
  min-height: 0;
  padding: 0;
  align-items: stretch;
  justify-content: stretch;
  appearance: none;
  border: 0;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  background: var(--tile-bg);
  cursor: pointer;
  touch-action: none;
}

.tile:nth-child(2n) {
  border-right: 0;
}

.tile:nth-child(n + 3) {
  border-bottom: 0;
}

.tile:focus-visible {
  z-index: 2;
  outline: 3px solid var(--accent);
  outline-offset: -3px;
}

.tile.drag-over::after,
.tile.swap-target::after,
.tile.selected-tile::after {
  position: absolute;
  content: "";
  inset: 0;
  border: 4px solid var(--accent);
  pointer-events: none;
}

.tile img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: cover;
  pointer-events: none;
}

.tile-empty {
  display: flex;
  flex: 1;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 10px;
  padding: 16px;
  text-align: center;
}

.tile-empty strong {
  color: var(--muted);
  font-size: 46px;
  line-height: 1;
}

.tile-empty span {
  color: var(--text);
  font-size: 14px;
  line-height: 1.2;
}

.legal {
  color: var(--muted);
}

.controls-panel {
  grid-column: 2;
  align-self: start;
  display: grid;
  align-content: start;
  gap: 18px;
  padding: 16px;
}

.button-stack {
  display: grid;
  gap: 10px;
}

button,
.primary-button,
.secondary-button {
  min-height: 38px;
  border: 1px solid var(--line-strong);
  border-radius: 8px;
  cursor: pointer;
  transition:
    background-color 160ms ease,
    border-color 160ms ease,
    transform 120ms ease;
}

button:active {
  transform: translateY(1px);
}

.primary-button {
  color: var(--accent-text);
  border-color: var(--accent-dark);
  background: var(--accent);
  font-weight: 700;
}

.primary-button:hover {
  background: var(--accent-dark);
}

#export-button {
  margin-top: 8px;
}

.secondary-button {
  background: var(--button-bg);
  color: var(--text);
}

.secondary-button:hover {
  border-color: var(--accent);
  background: var(--button-hover);
}

.legal {
  width: min(100%, var(--layout-width));
  margin: 0 auto;
  display: flex;
  flex-wrap: wrap;
  gap: 8px 18px;
  padding: 18px 0 0;
  font-size: 12px;
}

@media (max-width: 940px) {
  :root {
    --layout-width: var(--cover-column);
  }

  .workspace {
    grid-template-columns: minmax(0, var(--cover-column));
    justify-content: center;
  }

  .controls-panel {
    grid-column: auto;
    grid-row: auto;
    justify-self: center;
    width: min(100%, 320px);
  }

  .cover-panel {
    grid-row: auto;
    width: 100%;
  }
}

@media (max-width: 680px) {
  .app-shell {
    width: min(100vw - 20px, 1180px);
    padding-top: 12px;
  }

  .cover-panel {
    min-height: 0;
    padding: 12px;
  }

  .cover-grid {
    width: min(100%, 440px);
  }

  .topbar {
    align-items: flex-start;
    flex-direction: column;
  }
}