html {
    box-sizing: border-box;
}

body {
    margin: 0;
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background: linear-gradient(to right, #4ca1af, #c4e0e5);
}

/* =============== Calculator =============== */

.calculator {
    background: #121212;
    width: 400px;
    border-radius: 12px;
    box-shadow: 0 5px 30px -5px rgba(0, 0, 0, 0.6);
}

/*  =============== Display =============== */
.calculator-display {
    background: #121212;
    color: white;
    margin: 0;
    display: flex;
    align-items: center;
    justify-content: flex-end;
    border-radius: 10px 10px 0 0;
}

.calculator-display h1 {
    margin: 0;
    padding: 25px;
    font-size: 45px;
    font-family: 'Lucida Console', sans-serif;
    font-weight: 100;
    overflow-x: auto;
}

/* =============== Custom Scrollbar =============== */

::-webkit-scrollbar {
    width: 10px;
  }

  ::-webkit-scrollbar-track {
    background: #f1f1f1;
  }

  ::-webkit-scrollbar-thumb {
    background: #888;
  }

  ::-webkit-scrollbar-thumb:hover {
    background: #555;
  }

  /* =============== Buttons =============== */
  .calculator-buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-gap: 10px;
    padding: 10px;
  }

  button {
      min-height: 50px;
      font-size: 20px;
      font-weight: 100;
      border: none;
      border-radius: 5px;
      cursor: pointer;
      background: #30475e;
      color: white;
  }

  button:hover {
      filter: brightness(110%);
  }

  button:active {
      transform: translateY(1px);
  }

  button:focus {
      outline:none;
  }

  .operator {
      background: #f05454;
      color: white;
      font-size: 22px;
  }

  .clear {
      background: #f05454;
      color: white;
  }

  .equal-sign {
      grid-column: -2;
      grid-row: 2 / span 4;
      background: #f5f5f5;
      color: black;
  }

/* Media Query: Large Smartphone (Vertical) */
@media screen and (max-width: 600px) {
    .calculator {
        width: 95%;
    }
}