body {
      display: flex;
      justify-content: center;
      align-items: center;
      height: 100vh;
      margin: 0;
      background: linear-gradient(135deg, #74b9ff, #81ecec);
      font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
    }

    .calculator {
      background: #ffffff;
      padding: 38px;
      border-radius: 20px;
      box-shadow: 0px 8px 25px rgba(0, 0, 0, 0.25);
      width: 500px; /* made longer */
      text-align: center;
    }

    .logo {
      font-size: 22px;
      font-weight: bold;
      margin-bottom: 15px;
      color: #0984e3;
      letter-spacing: 1px;
    }

    #display {
      width: 100%;
      height: 60px;
      font-size: 28px;
      margin-bottom: 20px;
      padding: 10px;
      border: none;
      border-radius: 12px;
      background: #f1f2f6;
      text-align: right;
      font-weight: bold;
      color: #2d3436;
    }

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

    button {
      padding: 20px;
      font-size: 20px;
      font-weight: bold;
      border: none;
      border-radius: 12px;
      cursor: pointer;
      background: #dfe6e9;
      transition: all 0.2s ease-in-out;
    }

    button:hover {
      transform: scale(1.05);
      background: #b2bec3;
    }

    .operator { background: #0984e3; color: white; }
    .equal { grid-column: span 2; background: #00cec9; color: white; }
    .clear { background: #ff7675; color: white; }