* { margin: 0; padding: 0; box-sizing: border-box; }

  body {
    min-height: 100vh;
    display: grid;
    place-items: center;
    padding: 24px;
    font-family: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI",
                 Roboto, Helvetica, Arial, sans-serif;
    color: #e8eaed;
    background: radial-gradient(circle at 30% 0%, #232a38 0%, #0b0d11 60%);
  }

  /* ---------- Shell ---------- */
  .calculator {
    width: min(360px, 100%);
    padding: 22px;
    border-radius: 32px;
    background: linear-gradient(160deg, #1c2027, #14171d);
    border: 1px solid rgba(255, 255, 255, 0.06);
    box-shadow:
      0 30px 60px -20px rgba(0, 0, 0, 0.85),
      0 0 0 1px rgba(0, 0, 0, 0.4),
      inset 0 1px 0 rgba(255, 255, 255, 0.07);
  }

  /* ---------- Display ---------- */
  .display {
    text-align: right;
    padding: 26px 12px 22px;
    margin-bottom: 18px;
  }

  
  .result {
    font-size: 2.75rem;
    font-weight: 600;
    line-height: 1;
    letter-spacing: -1.5px;
    color: #ffffff;
    text-shadow: 0 2px 12px rgba(255, 255, 255, 0.08);
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
  }

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

  .key {
    aspect-ratio: 1;
    display: grid;
    place-items: center;
    font: inherit;
    font-size: 1.25rem;
    font-weight: 500;
    color: #e8eaed;
    background: #262b34;
    border: none;
    border-radius: 50%;
    cursor: pointer;
    -webkit-tap-highlight-color: transparent;
    box-shadow:
      0 2px 0 rgba(0, 0, 0, 0.35),
      inset 0 1px 0 rgba(255, 255, 255, 0.06);
    transition: background 0.18s ease, transform 0.08s ease,
                box-shadow 0.18s ease;
  }

  .key:hover  { background: #313843; }
  .key:active {
    transform: scale(0.93);
    background: #3a4250;
    box-shadow: inset 0 2px 6px rgba(0, 0, 0, 0.5);
  }

  .key:focus-visible {
    outline: 2px solid #ff8a3d;
    outline-offset: 3px;
  }

  /* Function keys: AC, ±, % */
  .key.fn {
    background: #3a4150;
    color: #dbe2ec;
    font-size: 1.1rem;
  }
  .key.fn:hover  { background: #454d5e; }
  .key.fn:active { background: #505a6d; }

  /* Operator keys */
  .key.op {
    font-size: 1.4rem;
    color: #ffffff;
    background: linear-gradient(145deg, #ff9d5c, #ff7a26);
    box-shadow:
      0 2px 0 rgba(150, 60, 0, 0.5),
      inset 0 1px 0 rgba(255, 255, 255, 0.35);
  }
  .key.op:hover  { background: linear-gradient(145deg, #ffab73, #ff8a3d); }
  .key.op:active { background: linear-gradient(145deg, #f08a45, #e56a15); }

  /* Zero key spans two columns */
  .key.zero {
    grid-column: span 2;
    aspect-ratio: auto;
    border-radius: 999px;
    justify-items: center;
  }

  /* ---------- Small screens ---------- */
  @media (max-width: 380px) {
    .calculator { padding: 16px; border-radius: 26px; }
    .keys { gap: 9px; }
    .result { font-size: 2.2rem; }
    .key { font-size: 1.1rem; }
  }