:root {
  --category_1: #f59e0b;
  --category_2: #3b82f6;
  --category_3: #22c55e;
  --category_4: #ef4444;

  --category_1-glow: rgba(245, 158, 11, 0.35);
  --category_2-glow: rgba(59, 130, 246, 0.35);
  --category_3-glow: rgba(34, 197, 94, 0.35);
  --category_4-glow: rgba(239, 68, 68, 0.35);

  --bg-overlay: rgba(15, 23, 42, 0.55);
  --column-bg: rgba(15, 23, 42, 0.55);
  --column-border: rgba(255, 255, 255, 0.08);
  --card-bg: rgba(30, 41, 59, 0.85);
  --card-bg-hover: rgba(51, 65, 85, 0.9);
  --text-primary: #f8fafc;
  --text-muted: rgba(248, 250, 252, 0.6);
  --text-faint: rgba(248, 250, 252, 0.35);

  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;

  --shadow-sm: 0 2px 6px rgba(0, 0, 0, 0.25);
  --shadow-md: 0 8px 20px rgba(0, 0, 0, 0.35);
  --shadow-lg: 0 12px 40px rgba(0, 0, 0, 0.45);

  --transition: 180ms cubic-bezier(0.4, 0, 0.2, 1);
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  padding: 0;
  min-height: 100vh;
}

body {
  font-family: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    sans-serif;
  color: var(--text-primary);
  background:
    linear-gradient(135deg, rgba(15, 23, 42, 0.6), rgba(15, 23, 42, 0.85)),
    radial-gradient(ellipse at top, #1e293b 0%, #0f172a 100%);
  background-attachment: fixed;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* ---------- Header ---------- */

.app-header {
  text-align: center;
  padding: 2.5rem 1rem 1.5rem;
}

.main-title {
  margin: 0;
  font-size: clamp(1.75rem, 4vw, 2.75rem);
  font-weight: 800;
  letter-spacing: -0.02em;
  background: linear-gradient(135deg, #f8fafc 0%, #94a3b8 100%);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

.subtitle {
  margin: 0.5rem 0 0;
  color: var(--text-muted);
  font-size: clamp(0.875rem, 1.5vw, 1rem);
  font-weight: 400;
}

/* ---------- Layout ---------- */

ul {
  list-style: none;
  margin: 0;
  padding: 0;
}

.drag-container {
  padding: 0 clamp(0.75rem, 2vw, 1.5rem) 2rem;
  max-width: 1600px;
  margin: 0 auto;
}

.drag-list {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: clamp(0.75rem, 1.5vw, 1.25rem);
  align-items: flex-start;
}

/* ---------- Column ---------- */

.drag-column {
  background: var(--column-bg);
  border: 1px solid var(--column-border);
  border-radius: var(--radius-lg);
  padding: 0.75rem;
  display: flex;
  flex-direction: column;
  min-height: 200px;
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  box-shadow: var(--shadow-md);
  transition: border-color var(--transition), box-shadow var(--transition);
}

.drag-column.over {
  border-color: rgba(255, 255, 255, 0.4);
  box-shadow: var(--shadow-lg);
}

.header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.5rem 0.75rem;
  margin-bottom: 0.5rem;
  border-radius: var(--radius-md);
  background: rgba(255, 255, 255, 0.04);
}

.header-info {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  min-width: 0;
}

.header h2 {
  margin: 0;
  font-size: 0.95rem;
  font-weight: 600;
  letter-spacing: 0.02em;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.header-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  flex-shrink: 0;
}

.count {
  font-size: 0.75rem;
  font-weight: 600;
  color: var(--text-muted);
  background: rgba(255, 255, 255, 0.08);
  padding: 0.15rem 0.5rem;
  border-radius: 999px;
  min-width: 1.5rem;
  text-align: center;
}

[data-column="backlog"] .header-dot { background: var(--category_1); box-shadow: 0 0 12px var(--category_1-glow); }
[data-column="progress"] .header-dot { background: var(--category_2); box-shadow: 0 0 12px var(--category_2-glow); }
[data-column="complete"] .header-dot { background: var(--category_3); box-shadow: 0 0 12px var(--category_3-glow); }
[data-column="reject"] .header-dot { background: var(--category_4); box-shadow: 0 0 12px var(--category_4-glow); }

[data-column="backlog"] { border-top: 3px solid var(--category_1); }
[data-column="progress"] { border-top: 3px solid var(--category_2); }
[data-column="complete"] { border-top: 3px solid var(--category_3); }
[data-column="reject"] { border-top: 3px solid var(--category_4); }

/* ---------- Add Button ---------- */

.add-btn {
  width: 28px;
  height: 28px;
  border-radius: 8px;
  border: none;
  background: rgba(255, 255, 255, 0.08);
  color: var(--text-primary);
  font-size: 1.25rem;
  font-weight: 400;
  line-height: 1;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background var(--transition), transform var(--transition);
  flex-shrink: 0;
}

.add-btn:hover,
.add-btn:focus-visible {
  background: rgba(255, 255, 255, 0.18);
  transform: scale(1.05);
  outline: none;
}

.add-btn:active {
  transform: scale(0.95);
}

/* ---------- Scroll Area ---------- */

.custom-scroll {
  overflow-y: auto;
  max-height: 60vh;
  flex: 1;
  padding-right: 4px;
  position: relative;
}

.custom-scroll::-webkit-scrollbar {
  width: 6px;
}

.custom-scroll::-webkit-scrollbar-track {
  background: transparent;
}

.custom-scroll::-webkit-scrollbar-thumb {
  background: rgba(255, 255, 255, 0.15);
  border-radius: 3px;
}

.custom-scroll::-webkit-scrollbar-thumb:hover {
  background: rgba(255, 255, 255, 0.25);
}

.drag-item-list {
  min-height: 60px;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.empty-state {
  text-align: center;
  color: var(--text-faint);
  font-size: 0.85rem;
  font-style: italic;
  margin: 0.75rem 0 0.25rem;
  pointer-events: none;
  display: none;
}

.drag-item-list:empty + .empty-state {
  display: block;
}

/* ---------- Card ---------- */

.drag-item {
  position: relative;
  padding: 0.75rem 2rem 0.75rem 0.85rem;
  background: var(--card-bg);
  border: 1px solid rgba(255, 255, 255, 0.06);
  border-radius: var(--radius-md);
  font-size: 0.9rem;
  line-height: 1.45;
  letter-spacing: 0.01em;
  cursor: grab;
  box-shadow: var(--shadow-sm);
  transition: background var(--transition), transform var(--transition),
    box-shadow var(--transition), opacity var(--transition);
  word-break: break-word;
  animation: cardIn 220ms ease-out;
}

@keyframes cardIn {
  from { opacity: 0; transform: translateY(-4px); }
  to { opacity: 1; transform: translateY(0); }
}

.drag-item:hover {
  background: var(--card-bg-hover);
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

.drag-item:active {
  cursor: grabbing;
}

.drag-item.dragging {
  opacity: 0.4;
  transform: scale(0.97);
}

.drag-item-text {
  display: block;
  outline: none;
  border-radius: 4px;
  min-height: 1.2em;
}

.drag-item-text:focus {
  background: rgba(255, 255, 255, 0.06);
  box-shadow: 0 0 0 2px rgba(59, 130, 246, 0.4);
  cursor: text;
}

.delete-btn {
  position: absolute;
  top: 0.4rem;
  right: 0.4rem;
  width: 22px;
  height: 22px;
  border-radius: 6px;
  border: none;
  background: transparent;
  color: var(--text-faint);
  font-size: 1rem;
  line-height: 1;
  cursor: pointer;
  opacity: 0;
  transition: opacity var(--transition), background var(--transition),
    color var(--transition);
  display: flex;
  align-items: center;
  justify-content: center;
}

.drag-item:hover .delete-btn,
.drag-item:focus-within .delete-btn {
  opacity: 1;
}

.delete-btn:hover,
.delete-btn:focus-visible {
  background: rgba(239, 68, 68, 0.2);
  color: #fca5a5;
  outline: none;
}

/* ---------- Responsive ---------- */

@media (max-width: 1024px) {
  .drag-list {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
  .custom-scroll {
    max-height: 50vh;
  }
}

@media (max-width: 640px) {
  .app-header {
    padding: 1.5rem 1rem 1rem;
  }
  .drag-list {
    grid-template-columns: 1fr;
  }
  .drag-column {
    min-height: auto;
  }
  .custom-scroll {
    max-height: none;
  }
  .delete-btn {
    opacity: 1;
  }
}

@media (hover: none) {
  .delete-btn {
    opacity: 1;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}