/* ───────────────────────────────────────────
   Reset & Custom Properties
─────────────────────────────────────────── */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --clr-bg: #0f172a;
  --clr-surface: #1e293b;
  --clr-surface-2: #334155;
  --clr-accent: #6366f1;
  --clr-accent-hover: #4f46e5;
  --clr-success: #22c55e;
  --clr-text: #f1f5f9;
  --clr-text-muted: #94a3b8;
  --clr-card-back: #334155;
  --clr-card-front: #6366f1;
  --clr-card-matched: #16a34a;
  --radius: 12px;
  --card-size: clamp(70px, 18vw, 110px);
  --gap: clamp(8px, 2vw, 14px);
  --transition: 0.3s ease;
}

/* ───────────────────────────────────────────
   Base
─────────────────────────────────────────── */
body {
  background: var(--clr-bg);
  color: var(--clr-text);
  font-family: 'Segoe UI', system-ui, sans-serif;
  min-height: 100dvh;
  display: flex;
  justify-content: center;
  align-items: flex-start;
}

.app {
  width: 100%;
  max-width: 640px;
  padding: 24px 16px 48px;
}

/* ───────────────────────────────────────────
   Header
─────────────────────────────────────────── */
.header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 12px;
  margin-bottom: 28px;
}

.title {
  font-size: clamp(1.4rem, 5vw, 2rem);
  font-weight: 700;
  letter-spacing: -0.5px;
  background: linear-gradient(135deg, #818cf8, #6366f1);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.stats {
  display: flex;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
}

.stat {
  font-size: 0.9rem;
  color: var(--clr-text-muted);
}

.stat strong {
  color: var(--clr-text);
}

/* ───────────────────────────────────────────
   Buttons
─────────────────────────────────────────── */
.btn-reset,
.btn-primary {
  background: var(--clr-accent);
  color: #fff;
  border: none;
  border-radius: 8px;
  padding: 8px 18px;
  font-size: 0.875rem;
  font-weight: 600;
  cursor: pointer;
  transition: background var(--transition), transform var(--transition);
}

.btn-reset:hover,
.btn-primary:hover {
  background: var(--clr-accent-hover);
  transform: translateY(-1px);
}

.btn-reset:active,
.btn-primary:active {
  transform: translateY(0);
}

.btn-primary {
  padding: 12px 32px;
  font-size: 1rem;
}

/* ───────────────────────────────────────────
   Board
─────────────────────────────────────────── */
.board-wrapper {
  display: flex;
  justify-content: center;
}

.board {
  display: grid;
  grid-template-columns: repeat(4, var(--card-size));
  gap: var(--gap);
}

/* ───────────────────────────────────────────
   Card
─────────────────────────────────────────── */
.card {
  width: var(--card-size);
  height: var(--card-size);
  perspective: 800px;
  cursor: pointer;
  border-radius: var(--radius);
}

.card-inner {
  width: 100%;
  height: 100%;
  position: relative;
  transform-style: preserve-3d;
  transition: transform 0.5s cubic-bezier(0.4, 0, 0.2, 1);
  border-radius: var(--radius);
}

/* Flipped state */
.card.flipped .card-inner {
  transform: rotateY(180deg);
}

.card-face {
  position: absolute;
  inset: 0;
  border-radius: var(--radius);
  display: flex;
  align-items: center;
  justify-content: center;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
}

/* Back face (default visible) */
.card-back {
  background: var(--clr-card-back);
  box-shadow: 0 4px 12px rgba(0,0,0,0.3);
  border: 2px solid rgba(255,255,255,0.06);
  font-size: calc(var(--card-size) * 0.38);
  color: var(--clr-text-muted);
}

.card-back::after {
  content: '?';
  font-weight: 700;
}

/* Front face (shown when flipped) */
.card-front {
  background: var(--clr-card-front);
  transform: rotateY(180deg);
  font-size: calc(var(--card-size) * 0.48);
  box-shadow: 0 4px 16px rgba(99,102,241,0.4);
  border: 2px solid rgba(255,255,255,0.12);
}

/* Matched card */
.card.matched .card-inner {
  transform: rotateY(180deg);
}

.card.matched .card-front {
  background: var(--clr-card-matched);
  box-shadow: 0 4px 16px rgba(34,197,94,0.4);
  border-color: rgba(255,255,255,0.15);
}

/* Disabled overlay while comparing */
.board.locked .card:not(.flipped):not(.matched) {
  pointer-events: none;
  opacity: 0.85;
}

/* Keyboard focus indicator */
.card:focus-visible {
  outline: 2px solid var(--clr-accent);
  outline-offset: 3px;
}

/* Hover glow on unflipped, unlocked cards */
.board:not(.locked) .card:not(.flipped):not(.matched):hover .card-back {
  border-color: rgba(99,102,241,0.5);
  box-shadow: 0 0 0 2px rgba(99,102,241,0.25), 0 4px 12px rgba(0,0,0,0.3);
}

/* ───────────────────────────────────────────
   Win Modal
─────────────────────────────────────────── */
.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.65);
  backdrop-filter: blur(4px);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 100;
  animation: fadeIn 0.25s ease;
}

.modal-overlay[hidden] {
  display: none;
}

.modal {
  background: var(--clr-surface);
  border: 1px solid var(--clr-surface-2);
  border-radius: 20px;
  padding: 40px 36px;
  text-align: center;
  max-width: 340px;
  width: calc(100% - 32px);
  box-shadow: 0 24px 60px rgba(0,0,0,0.5);
  animation: slideUp 0.3s cubic-bezier(0.34, 1.56, 0.64, 1);
}

.modal-icon {
  font-size: 3rem;
  margin-bottom: 12px;
}

.modal-title {
  font-size: 1.75rem;
  font-weight: 700;
  margin-bottom: 10px;
}

.modal-body {
  color: var(--clr-text-muted);
  margin-bottom: 28px;
  line-height: 1.6;
}

.modal-body strong {
  color: var(--clr-text);
}

/* ───────────────────────────────────────────
   Animations
─────────────────────────────────────────── */
@keyframes fadeIn {
  from { opacity: 0; }
  to   { opacity: 1; }
}

@keyframes slideUp {
  from { opacity: 0; transform: translateY(30px) scale(0.95); }
  to   { opacity: 1; transform: translateY(0) scale(1); }
}

@keyframes bounce {
  0%, 100% { transform: rotateY(180deg) scale(1); }
  50%       { transform: rotateY(180deg) scale(1.08); }
}

.card.matched .card-inner {
  animation: bounce 0.4s ease 0.1s;
}

/* ───────────────────────────────────────────
   Responsive
─────────────────────────────────────────── */
@media (max-width: 400px) {
  .header {
    flex-direction: column;
    align-items: flex-start;
  }
}