:root {
  /* Colors */
  --bg-color: #F3F4F6;
  --card-bg: #FFFFFF;
  --primary: #4F46E5; /* Indigo */
  --primary-hover: #4338CA;
  --accent: #F59E0B; /* Amber for hints */
  --danger: #EF4444; /* Red for alert */
  --danger-bg: #FEE2E2;
  --text-main: #111827;
  --text-muted: #6B7280;
  --border-color: #E5E7EB;
  
  /* Levels */
  --level-3: #10B981; /* Emerald */
  --level-2: #F59E0B; /* Amber */
  --level-1: #EF4444; /* Red */

  /* Spacing */
  --spacing-sm: 8px;
  --spacing-md: 16px;
  --spacing-lg: 24px;
  --spacing-xl: 32px;
}

* {
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background-color: var(--bg-color);
  color: var(--text-main);
  margin: 0;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  line-height: 1.5;
}

/* Layout */
.navbar {
  background: var(--card-bg);
  border-bottom: 1px solid var(--border-color);
  padding: var(--spacing-md) var(--spacing-xl);
  display: flex;
  justify-content: space-between;
  align-items: center;
  position: sticky;
  top: 0;
  z-index: 100;
}

.brand {
  font-weight: 700;
  font-size: 1.25rem;
  color: var(--primary);
  text-decoration: none;
}

.main-container {
  max-width: 600px;
  margin: 0 auto;
  padding: var(--spacing-xl) var(--spacing-md);
  width: 100%;
  flex-grow: 1;
  display: flex;
  flex-direction: column;
  justify-content: center;
}

/* Card */
.card {
  background: var(--card-bg);
  border-radius: 16px;
  box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.1), 0 8px 10px -6px rgba(0, 0, 0, 0.1);
  padding: var(--spacing-xl);
  text-align: center;
  overflow: hidden;
  transition: transform 0.2s;
}

/* Typography */
h1 {
  font-size: 1.875rem;
  font-weight: 800;
  margin-top: 0;
  margin-bottom: var(--spacing-md);
  color: var(--text-main);
}

h2 {
  font-size: 1.5rem;
  font-weight: 700;
  margin-bottom: var(--spacing-md);
}

p {
  color: var(--text-muted);
  margin-bottom: var(--spacing-lg);
}

.instruction {
  font-size: 1.125rem;
  font-weight: 500;
  color: var(--text-main);
  margin-bottom: var(--spacing-lg);
}

/* Memory Grid */
.memory-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 12px;
  background: var(--bg-color);
  padding: 12px;
  border-radius: 16px;
  margin: 0 auto var(--spacing-lg);
  max-width: 320px;
  aspect-ratio: 1 / 1;
}

.grid-cell {
  background: var(--card-bg);
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 2rem;
  font-weight: 700;
  color: var(--primary);
  box-shadow: 0 2px 4px rgba(0,0,0,0.05);
  cursor: default;
  position: relative;
  transition: all 0.2s ease;
  user-select: none;
}

.grid-cell.empty {
  background: #E5E7EB;
  color: transparent;
  cursor: pointer;
}

.grid-cell.empty:hover {
  background: #D1D5DB;
}

.grid-cell.filled {
  background: var(--card-bg);
  color: var(--text-main);
  border: 2px solid var(--primary);
}

.grid-cell.hint-reveal {
  background: #FEF3C7; /* Amber bg */
  color: #D97706; /* Amber text */
  border: 2px solid #F59E0B;
  animation: pulse 2s infinite;
}

/* Controls */
.controls-row {
  display: flex;
  justify-content: space-between;
  gap: var(--spacing-md);
  margin-top: var(--spacing-lg);
}

.number-pad {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 8px;
  margin-top: var(--spacing-lg);
}

.num-btn {
  background: var(--card-bg);
  border: 1px solid var(--border-color);
  border-radius: 8px;
  padding: 12px;
  font-size: 1.25rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.1s;
}

.num-btn:hover {
  background: var(--bg-color);
  transform: translateY(-2px);
}

.num-btn:active {
  transform: translateY(0);
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 12px 24px;
  border-radius: 12px;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
  border: none;
  font-size: 1rem;
  text-decoration: none;
  width: 100%;
}

.btn-primary {
  background: var(--primary);
  color: white;
  box-shadow: 0 4px 14px rgba(79, 70, 229, 0.4);
}

.btn-primary:hover {
  background: var(--primary-hover);
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(79, 70, 229, 0.6);
}

.btn-secondary {
  background: white;
  color: var(--text-main);
  border: 1px solid var(--border-color);
}

.btn-secondary:hover {
  background: var(--bg-color);
  border-color: #D1D5DB;
}

.btn-hint {
  background: #FFFBEB;
  color: #B45309;
  border: 1px solid #FCD34D;
}

.btn-hint:hover {
  background: #FEF3C7;
}

.btn-danger {
  background: white;
  color: var(--danger);
  border: 1px solid var(--danger);
}

.btn-danger:hover {
  background: var(--danger-bg);
}

/* Alert States */
.red-alert-screen {
  background: #FEF2F2;
  border: 2px solid var(--danger);
  animation: shake 0.5s ease-in-out;
}

.red-alert-screen h1 {
  color: var(--danger);
}

.alert-badge {
  display: inline-block;
  padding: 4px 12px;
  border-radius: 99px;
  font-size: 0.875rem;
  font-weight: 700;
  text-transform: uppercase;
  margin-bottom: var(--spacing-md);
}

.badge-danger {
  background: var(--danger);
  color: white;
}

.badge-success {
  background: var(--level-3);
  color: white;
}

.badge-warning {
  background: var(--level-2);
  color: white;
}

/* Timer */
.timer-container {
  width: 100%;
  height: 6px;
  background: #E5E7EB;
  border-radius: 3px;
  margin-bottom: var(--spacing-xl);
  overflow: hidden;
}

.timer-bar {
  height: 100%;
  background: var(--primary);
  width: 100%;
  transform-origin: left;
  animation: countdown 5s linear forwards;
}

@keyframes countdown {
  from { transform: scaleX(1); }
  to { transform: scaleX(0); }
}

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-5px); }
  75% { transform: translateX(5px); }
}

@keyframes pulse {
  0% { box-shadow: 0 0 0 0 rgba(245, 158, 11, 0.4); }
  70% { box-shadow: 0 0 0 10px rgba(245, 158, 11, 0); }
  100% { box-shadow: 0 0 0 0 rgba(245, 158, 11, 0); }
}

/* Utilities */
.text-center { text-align: center; }
.mb-4 { margin-bottom: 1rem; }
.mt-4 { margin-top: 1rem; }
.w-full { width: 100%; }

/* Text Colors */
.text-primary { color: var(--primary); }
.text-danger { color: var(--danger); }
.text-accent { color: var(--accent); }
.text-muted { color: var(--text-muted); }
.text-main { color: var(--text-main); }

/* Borders */
.border-primary { border-color: var(--primary) !important; }

/* Opacity */
.opacity-80 { opacity: 0.8; }

/* Font Weights */
.fw-600 { font-weight: 600; }

.stats-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 16px;
    margin-bottom: 24px;
}

.stat-box {
    background: #F9FAFB;
    padding: 16px;
    border-radius: 12px;
    text-align: center;
}

.stat-value {
    display: block;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-main);
}

.stat-label {
    font-size: 0.875rem;
    color: var(--text-muted);
}