.s15-grid {
  display: grid; gap: 6px; margin: 0 auto; width: max-content;
  background: var(--surface-2); padding: 8px; border-radius: var(--radius-sm);
}
.s15-cell {
  width: 64px; height: 64px; min-width: 64px; min-height: 64px;
  border: none; border-radius: 12px; font-size: 26px; font-weight: 900; color: var(--ink);
  background: linear-gradient(180deg, #fff, #ffe9f4);
  box-shadow: var(--shadow-sm); cursor: pointer; transition: transform .08s ease;
}
.s15-cell:active { transform: scale(.94); }
.s15-cell.blank { background: transparent; box-shadow: none; cursor: default; }
.s15-cell.correct { background: linear-gradient(180deg, #d6fff0, #b6f5e0); }
@media (max-width: 380px) {
  .s15-cell { width: 54px; height: 54px; min-width: 54px; min-height: 54px; font-size: 22px; }
}