:root {
  --bg: #eef2f6;
  --border: #8a8a8a;
  --accent: #2f6fab;
  --accent-dark: #1f4f7f;
  --header-blue: #5b9bd5;
  --shadow: 0 6px 18px rgba(20, 40, 80, 0.14);
  --board-padding: 16px;
  --col-gap: 10px;
  --grid-line: #dde4ec;
  --board-bg: #f8fafc;
  --guide-color: #7b8fa4;
  --guide-width: 2px;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  height: 100%;
  overflow: hidden;
  font-family: "Segoe UI", system-ui, sans-serif;
  background: var(--bg);
  color: #1f2933;
}

.scroll-container {
  height: 100%;
  overflow-x: hidden;
  overflow-y: scroll;
  touch-action: pan-y;
  scrollbar-gutter: stable;
  -webkit-overflow-scrolling: touch;
}

.scroll-container::-webkit-scrollbar {
  width: 14px;
}

.scroll-container::-webkit-scrollbar-track {
  background: #e2e8f0;
}

.scroll-container::-webkit-scrollbar-thumb {
  background: #94a3b8;
  border-radius: 8px;
  border: 3px solid #e2e8f0;
}

.scroll-container::-webkit-scrollbar-thumb:hover {
  background: #64748b;
}

.board-page {
  position: relative;
  min-height: 100%;
  background:
    linear-gradient(var(--grid-line) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid-line) 1px, transparent 1px),
    var(--board-bg);
  background-size: 32px 32px;
  background-attachment: fixed;
}

.column-guides {
  position: absolute;
  inset: 0;
  display: grid;
  grid-template-columns: 1fr 1fr 3fr;
  gap: var(--col-gap);
  padding: 0 var(--board-padding);
  pointer-events: none;
  z-index: 0;
}

.column-guides .guide:not(:last-child),
.header-guides .guide:not(:last-child) {
  border-right: var(--guide-width) dashed var(--guide-color);
}

.column-headers {
  position: sticky;
  top: 0;
  z-index: 30;
  display: grid;
  grid-template-columns: 1fr 1fr 3fr;
  gap: var(--col-gap);
  padding: 0.65rem var(--board-padding) 0.75rem;
  background: transparent;
}

.column-headers::after {
  content: "";
  position: absolute;
  left: var(--board-padding);
  right: var(--board-padding);
  bottom: 0;
  border-bottom: var(--guide-width) dashed var(--guide-color);
}

.header-guides {
  position: absolute;
  inset: 0;
  display: grid;
  grid-template-columns: 1fr 1fr 3fr;
  gap: var(--col-gap);
  padding: 0 var(--board-padding);
  pointer-events: none;
  z-index: 0;
}

.col-header {
  position: relative;
  z-index: 1;
  text-align: center;
  font-weight: 700;
  font-size: clamp(0.85rem, 1.6vw, 1.05rem);
  color: var(--header-blue);
  padding: 0.35rem 0.5rem;
}

.whiteboard {
  position: relative;
  width: 100%;
  min-height: 0;
  touch-action: pan-y;
  z-index: 1;
}

.card {
  position: absolute;
  width: clamp(95px, 10vw, 155px);
  aspect-ratio: 258 / 216;
  border: 1px solid var(--border);
  border-radius: 4px;
  background: white;
  box-shadow: var(--shadow);
  cursor: grab;
  touch-action: none;
  user-select: none;
  z-index: 1;
}

.card img {
  width: 100%;
  height: 100%;
  display: block;
  pointer-events: none;
}

.card.dragging {
  cursor: grabbing;
  box-shadow: 0 14px 28px rgba(20, 40, 80, 0.28);
}

.shuffle-btn {
  position: absolute;
  right: var(--board-padding);
  bottom: var(--board-padding);
  border: none;
  border-radius: 999px;
  padding: 0.65rem 1.1rem;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  background: var(--accent);
  color: white;
  min-height: 44px;
  z-index: 25;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.2s ease;
}

.shuffle-btn.visible {
  opacity: 1;
  pointer-events: auto;
}

.shuffle-btn:hover,
.shuffle-btn:focus-visible {
  background: var(--accent-dark);
}