/* Reset & base */
* {
    box-sizing: border-box;
  }
  
  body {
    margin: 0;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: #121212;
    color: #eee;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 20px;
  }
  
  .container {
    display: flex;
    gap: 30px;
    flex-wrap: wrap;
    max-width: 1000px;
    width: 100%;
  }
  
  /* Calculator */
  .calculator {
    background: linear-gradient(145deg, #b71c1c, #7f0000);
    border-radius: 25px;
    box-shadow: 0 0 30px #b71c1caa;
    padding: 25px;
    width: 350px;
    display: flex;
    flex-direction: column;
  }
  
  .display {
    background: #2a0000;
    border-radius: 15px;
    padding: 20px;
    font-size: 2.5rem;
    color: #ffebee;
    text-align: right;
    min-height: 60px;
    overflow-x: auto;
    font-weight: 700;
    user-select: none;
    margin-bottom: 25px;
  }
  
  .buttons {
    display: grid;
    grid-template-columns: repeat(6, 1fr);
    gap: 15px;
  }
  
  button {
    background: linear-gradient(145deg, #e53935, #b71c1c);
    border: none;
    border-radius: 15px;
    padding: 18px 0;
    font-size: 1.1rem;
    color: #fff;
    cursor: pointer;
    box-shadow: 0 5px 10px #7f0000cc;
    transition: all 0.25s ease;
    user-select: none;
  }
  
  button:hover {
    background: linear-gradient(145deg, #ffeb3b, #fbc02d);
    color: #121212;
    box-shadow: 0 6px 15px #ffeb3bcc;
    transform: scale(1.1);
  }
  
  button:active {
    transform: scale(0.95);
  }
  
  button.equal {
    grid-column: span 6;
    background: linear-gradient(145deg, #ffb300, #ff6f00);
    font-weight: 700;
    color: #121212;
    box-shadow: 0 5px 15px #ff6f00cc;
  }
  
  button.equal:hover {
    background: linear-gradient(145deg, #fff176, #ffca28);
    box-shadow: 0 6px 18px #fff176cc;
  }
  
  /* Sidebar */
  .sidebar {
    background: #1b1b1b;
    border-radius: 25px;
    padding: 25px;
    width: 280px;
    box-shadow: 0 0 30px #b71c1caa;
    display: flex;
    flex-direction: column;
    gap: 30px;
    user-select: none;
  }
  
  .sidebar h2 {
    margin-top: 0;
    margin-bottom: 15px;
    font-weight: 700;
    color: #ff5252;
    text-align: center;
  }
  
  /* History */
  .history {
    max-height: 280px;
    overflow-y: scroll;
  }
  
  #historyList {
    list-style: none;
    padding-left: 0;
    margin: 0 0 15px 0;
    max-height: 200px;
    overflow-y: auto;
    border: 1px solid #7f0000;
    border-radius: 10px;
    background: #2a0000;
  }
  
  #historyList li {
    padding: 8px 12px;
    border-bottom: 1px solid #7f0000;
    font-size: 0.95rem;
    color: #f44336;
  }
  
  #historyList li:last-child {
    border-bottom: none;
  }
  
  #clearHistoryBtn {
    width: 100%;
    background: #b71c1c;
    border: none;
    border-radius: 12px;
    padding: 10px;
    font-weight: 700;
    cursor: pointer;
    color: #fff;
    transition: all 0.25s ease;
  }
  
  #clearHistoryBtn:hover {
    background: #ffeb3b;
    color: #121212;
  }
  
  /* Timer */
  .timer {
    text-align: center;
  }
  
  #timerDisplay {
    font-size: 2rem;
    font-weight: 700;
    background: #2a0000;
    border-radius: 15px;
    padding: 15px 0;
    color: #ffeb3b;
    margin-bottom: 15px;
    user-select: none;
  }
  
  .timer-buttons button {
    background: #b71c1c;
    border: none;
    color: white;
    font-weight: 700;
    padding: 10px 18px;
    margin: 0 10px;
    border-radius: 12px;
    cursor: pointer;
    transition: all 0.25s ease;
    min-width: 80px;
  }
  
  .timer-buttons button:hover {
    background: #ffeb3b;
    color: #121212;
  }
  
  .timer-buttons button:active {
    transform: scale(0.95);
  }
  
  /* Responsive */
  @media (max-width: 800px) {
    .container {
      flex-direction: column;
      align-items: center;
    }
    .calculator, .sidebar {
      width: 100%;
      max-width: 400px;
    }
    .buttons {
      grid-template-columns: repeat(4, 1fr);
    }
    button.equal {
      grid-column: span 4;
    }
  }