* {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: 'Inter', sans-serif;
    }

    body {
      background: linear-gradient(135deg, #d9e4f5, #87a6d5);
      min-height: 100vh;
      display: flex;
      justify-content: center;
      align-items: center;
    }

    .calculator {
      background: #f9fcff;
      border-radius: 20px;
      box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
      padding: 20px;
      width: 360px;
    }

    .screen {
      background: #e4f0ff;
      border-radius: 10px;
      padding: 15px;
      margin-bottom: 20px;
      min-height: 70px;
      display: flex;
      flex-direction: column;
      justify-content: center;
    }

    .expression {
      font-size: 16px;
      color: #555;
      min-height: 20px;
    }

    .result {
      font-size: 28px;
      font-weight: 600;
      color: #1a1a1a;
      min-height: 30px;
    }

    .buttons {
      display: grid;
      grid-template-columns: repeat(4, 1fr);
      gap: 12px;
    }

    button {
      padding: 20px;
      border: none;
      border-radius: 10px;
      background-color: #d5e6fb;
      font-size: 18px;
      font-weight: 600;
      color: #1a1a1a;
      cursor: pointer;
      transition: background-color 0.2s;
    }

    button:hover {
      background-color: #bcd4f4;
    }

    .enter {
      background-color: #407ec9;
      color: #fff;
    }

    .enter:hover {
      background-color: #2e65a3;
    }

    .history {
      margin-top: 20px;
      background: #ffffff;
      border: 1px solid #ccc;
      padding: 10px;
      border-radius: 8px;
      max-height: 100px;
      overflow-y: auto;
      font-size: 14px;
    }