body {
  background-color: #121212;
  color: #eee;
}

/* ===================== */
/*      SUDOKU GRID      */
/* ===================== */
.grid-container {
  display: grid;
  margin: 20px auto;
  padding: 0;
  gap: 0;                  
  border-collapse: collapse;

  /* ✅ Ensure square layout */
  aspect-ratio: 1 / 1;     
  width: min(90vw, 500px); /* responsive: shrink on small, max 500px */
  
  --size: 9; /* updated in JS */
  grid-template-columns: repeat(var(--size), 1fr);
  grid-template-rows: repeat(var(--size), 1fr);
}

.big-btn {
  height: 70px;       /* ✅ double height */
  font-size: 1.3rem;  /* larger text */
  font-weight: bold;
}


.grid-cell {
  display: block;
  margin: 0 !important;
  padding: 0 !important;
  line-height: normal;
  text-align: center;
  vertical-align: middle;

  width: 100%;  /* ✅ fills its grid cell */
  height: 100%;
  
  background: #1a1a1a;
  color: #eee;
  border: 1px solid #333;
  font-size: clamp(12px, 3vw, 18px);
  box-sizing: border-box;
}

/* Remove number input arrows */
.grid-cell::-webkit-outer-spin-button,
.grid-cell::-webkit-inner-spin-button {
  -webkit-appearance: none;
  margin: 0;
}
.grid-cell[type=number] {
  -moz-appearance: textfield;
}

/* Subgrid thick borders */
.subgrid-top    { border-top: 3px solid #eee !important; }
.subgrid-left   { border-left: 3px solid #eee !important; }
.subgrid-right  { border-right: 3px solid #eee !important; }
.subgrid-bottom { border-bottom: 3px solid #eee !important; }

/* ===================== */
/*      CELL STATES      */
/* ===================== */
.try       { background-color: #194d19 !important; }
.backtrack { background-color: #4d1919 !important; }
.given     { font-weight: bold; background: #333 !important; }
.hint      { background-color: #003366 !important; font-weight: bold; }
.mistake   { background-color: #660000 !important; }
.correct   { background-color: #194d19 !important; }

.strategy-highlight {
  background-color: #666600 !important;
  animation: flash 1s ease-in-out;
}

@keyframes flash {
  0%   { background-color: #ffff99; }
  100% { background-color: #003366; }
}

/* ===================== */
/*     OPTIONS PANEL     */
/* ===================== */
.options-panel {
  background-color: #1e1e1e;
  border: 1px solid #333;
}

.options-panel h4 {
  border-bottom: 1px solid #333;
  padding-bottom: 0.5rem;
  margin-bottom: 1rem;
}