* {
  box-sizing: border-box;
}
:root {
  --bg: #0f1115;
  --panel: #171a21;
  --muted: #9aa4b2;
  --text: #e6edf3;
  --accent: #4aa3ff;
  --accent-2: #7bd389;
  --danger: #ff6b6b;
  /* 动画系统：统一缓动与时长 */
  --anim-ease: cubic-bezier(0.2, 0.8, 0.2, 1);
  --anim-ease-soft: cubic-bezier(0.25, 0.9, 0.2, 1);
  --anim-fast: 120ms;
  --anim-med: 180ms;
  --anim-slow: 260ms;
}
html,
body {
  height: 100%;
}
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font:
    14px/1.4 system-ui,
    -apple-system,
    Segoe UI,
    Roboto,
    Helvetica,
    Arial,
    "Apple Color Emoji",
    "Segoe UI Emoji";
}
.app-header {
  position: sticky;
  top: 0;
  z-index: 10;
  background: linear-gradient(
    180deg,
    rgba(15, 17, 21, 0.95),
    rgba(15, 17, 21, 0.85)
  );
  backdrop-filter: saturate(1.4) blur(6px);
  border-bottom: 1px solid #252a34;
}
.app-header h1 {
  margin: 0;
  padding: 12px 16px;
  font-size: 18px;
}
.controls {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  padding: 8px 12px 12px;
}
.control-group {
  display: flex;
  align-items: center;
  gap: 8px;
  background: var(--panel);
  padding: 6px 8px;
  border-radius: 10px;
  border: 1px solid #222838;
}
.control-group label {
  color: var(--muted);
}
select,
button,
input[type="checkbox"] {
  accent-color: var(--accent);
}
select,
button {
  background: #0f1320;
  color: var(--text);
  border: 1px solid #293148;
  border-radius: 8px;
  padding: 6px 10px;
}
button {
  cursor: pointer;
}
button:hover {
  border-color: var(--accent);
}
#toggleOriginal {
  background: #0f1320;
}
#restart {
  background: #10201a;
  border-color: #264e3f;
}
#restart:hover {
  border-color: var(--accent-2);
}
#timeDisplay,
#stepDisplay {
  padding: 2px 6px;
  background: #0e1220;
  border: 1px solid #293148;
  border-radius: 6px;
}

.app-main {
  display: flex;
  justify-content: center;
  padding: 16px;
}
#boardWrapper {
  width: min(92vw, 720px);
}
.board {
  position: relative;
  width: 100%;
  aspect-ratio: 1/1;
  background: linear-gradient(135deg, #0c0f17, #0b0e15);
  border: 1px solid #293148;
  border-radius: 12px;
  overflow: hidden;
}

.tile {
  position: absolute;
  /* 禁止选中文本，统一触控与鼠标体验 */
  -webkit-user-select: none;
  -ms-user-select: none;
  user-select: none;
  touch-action: none;
  border-radius: 6px;
  /* 移除默认立体阴影，避免相邻块产生高低落差视觉 */
  box-shadow: none;
  border: 1px solid rgba(255, 255, 255, 0.06);
  background-size: 100% 100%;
  background-repeat: no-repeat;
  cursor: grab;
  will-change: transform;
  -webkit-tap-highlight-color: transparent;
  backface-visibility: hidden;
}
.tile.selected {
  z-index: 1000;
}
.tile.dragging {
  /* 拖拽态视觉增强 */
  box-shadow: 0 8px 14px rgba(0, 0, 0, 0.45);
}
.tile.swap-target {
  /* 拖拽时指针所在图块弹起放大（不包括当前被拖拽图块） */
  transform: scale(1.06);
  z-index: 900;
}

/* 释放并发生交换时的弹起动画（一次性） */
.tile.swap-pop {
  animation: swapPop var(--anim-med) var(--anim-ease);
}
@keyframes swapPop {
  0% {
    transform: scale(1);
  }
  50% {
    transform: scale(1.06);
  }
  100% {
    transform: scale(1);
  }
}
.tile:active {
  cursor: grabbing;
}
.tile .label {
  position: absolute;
  left: 6px;
  top: 6px;
  font-size: 0.8rem;
  padding: 2px 6px;
  border-radius: 999px;
  background: rgba(0, 0, 0, 0.55);
  border: 1px solid rgba(255, 255, 255, 0.15);
  color: #e0e6f0;
}
.tile.ghost {
  opacity: 0.6;
}

.grid-guide {
  position: absolute;
  inset: 0;
  pointer-events: none;
}
.grid-guide .cell {
  position: absolute;
  border: 1px dashed rgba(255, 255, 255, 0.08);
}

/* 滑块模式：与经典一致，使用 left/top 过渡，避免高低落差视觉 */
.board.sliding .tile {
  transition:
    left var(--anim-med) var(--anim-ease),
    top var(--anim-med) var(--anim-ease),
    transform var(--anim-fast) var(--anim-ease);
}

/* 经典模式：交换移动更自然（left/top 过渡） */
.board:not(.sliding) .tile {
  transition:
    left var(--anim-med) var(--anim-ease),
    top var(--anim-med) var(--anim-ease),
    transform var(--anim-fast) var(--anim-ease);
}

/* 通关弹窗覆盖层与内容 */
.modal {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.6);
  display: grid;
  place-items: center;
}
.modal[hidden] {
  display: none;
}
.modal-content {
  position: relative;
  background: #0c0f17;
  border: 1px solid #293148;
  border-radius: 12px;
  padding: 12px;
  max-width: min(92vw, 640px);
}
.modal-content img {
  max-width: 100%;
  border-radius: 8px;
  display: block;
}
.modal-close {
  position: absolute;
  right: 10px;
  top: 10px;
  background: var(--danger);
  color: #fff;
  border: 1px solid #d44d4d;
  border-radius: 999px;
  padding: 4px 12px;
  cursor: pointer;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.35);
  font-weight: 600;
  font-size: 16px;
}
.modal-close:hover {
  filter: brightness(1.08);
  border-color: #ff8f8f;
}
.modal-close:focus-visible {
  outline: 2px solid #fff;
  outline-offset: 2px;
}
.modal-actions {
  display: flex;
  justify-content: flex-end;
  gap: 8px;
  margin-top: 10px;
}
.modal-actions button {
  background: #0f1320;
  color: var(--text);
  border: 1px solid #293148;
  border-radius: 8px;
  padding: 6px 10px;
}

/* 通关后禁用棋盘交互 */
.board.disabled {
  pointer-events: none;
}

/* Responsive tweaks */
@media (max-width: 640px) {
  .controls {
    gap: 6px;
  }
  .control-group {
    flex-wrap: wrap;
  }
}

/* 右下角悬浮 GIF 窗口 */
.float-box {
  position: fixed;
  right: 16px;
  bottom: 16px;
  z-index: 8;
  background: var(--panel);
  border: 1px solid #293148;
  border-radius: 12px;
  padding: 8px;
  box-shadow: 0 6px 20px rgba(0, 0, 0, 0.35);
}
.float-box img {
  display: block;
  max-width: 180px;
  max-height: 180px;
  border-radius: 8px;
}

/* 页脚区域 */
.app-footer {
  margin: 24px auto 16px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 6px;
  color: var(--muted);
}
.github-btn {
  background: #0f1320;
  color: var(--text);
  border: 1px solid #293148;
  border-radius: 8px;
  padding: 6px 12px;
  text-decoration: none;
}
.github-btn:hover {
  border-color: var(--accent);
}

/* 辅助：尊重用户的减少动画偏好 */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}