.page-header {
  text-align: center;
  margin-bottom: 20px;
}

.page-header h1 {
  font-size: clamp(1.5rem, 5vw, 2rem);
  margin-bottom: 5px;
}

.subtitle {
  color: #666;
  font-size: clamp(0.875rem, 2.5vw, 1rem);
  margin: 0;
}

.content-card {
  background: #fff;
  border-radius: 12px;
  box-shadow: 0 3px 10px rgba(0, 0, 0, 0.1);
  padding: clamp(15px, 4vw, 25px);
  max-width: 480px;
  width: 100%;
  margin: 10px auto;
}

.timer {
  font-size: clamp(1.5rem, 5vw, 2rem);
  color: #fb6f92;
  font-weight: bold;
  padding: clamp(0.75rem, 2vw, 1rem) clamp(1rem, 3vw, 2rem);
  background-color: #f5f7fa;
  border-radius: 10px;
  margin-bottom: 20px;
}

.sudoku-grid {
  display: grid;
  gap: 0;
  border: 3px solid #333;
  width: fit-content;
  max-width: 100%;
  margin: 0 auto 25px auto;
  aspect-ratio: 1;
}

.sudoku-grid.size-6 {
  grid-template-columns: repeat(6, minmax(40px, 60px));
  grid-template-rows: repeat(6, minmax(40px, 60px));
}

.sudoku-cell {
  width: 100%;
  height: 100%;
  border: 1px solid #999;
  text-align: center;
  font-size: clamp(1rem, 4vw, 1.5rem);
  padding: 0;
  outline: none;
  background-color: #fff;
  transition: background-color 0.2s ease;
}

.sudoku-cell:focus {
  background-color: #e8f0fe;
}

.sudoku-cell[value] {
  background-color: #f9f9f9;
  color: #555;
  font-weight: 600;
}

.cta-button {
  padding: clamp(10px, 2vw, 14px) clamp(16px, 4vw, 24px);
  font-size: clamp(0.9rem, 2.5vw, 1rem);
  border-radius: 8px;
  cursor: pointer;
  transition: all 0.3s ease;
}

@media (max-width: 400px) {
  .content-card {
    padding: 12px;
    margin: 5px;
  }
  
  .sudoku-grid {
    border: 2px solid #333;
    margin-bottom: 20px;
  }
  
  .sudoku-grid.size-6 {
    grid-template-columns: repeat(6, minmax(32px, 1fr));
    grid-template-rows: repeat(6, minmax(32px, 1fr));
  }
  
  .sudoku-cell {
    border: 0.5px solid #999;
  }
}

@media (min-width: 401px) and (max-width: 900px) {
  .sudoku-grid.size-6 {
    grid-template-columns: repeat(6, minmax(45px, 1fr));
    grid-template-rows: repeat(6, minmax(45px, 1fr));
  }
}

@media (min-width: 901px) {
  .content-card {
    max-width: 480px;
  }
  
  .page-header h1 {
    font-size: 2rem;
  }
  
  .subtitle {
    font-size: 1rem;
  }
}