body {
  margin: 0;
  padding: 0;
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: linear-gradient(135deg, #1e1e2f, #2c2c54);
}

button {
  height: 100px;
  width: 100px;
  border: none;
  border-radius: 50%;
  background-color: #3a3a4f;
  color: #fff;
  font-size: 3rem;
  font-weight: bold;
  cursor: pointer;
}

button:hover {
  background-color: #4a4a65;
}
button:active {
  background-color: #5a5a7f;
}

#key {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
  padding: 25px;
}

#calculator {
  font-family: Arial, Helvetica, sans-serif;
  background-color: #2b2b3c;
  box-shadow: 0 20px 40px rgba(0, 0, 0, 0.6);
  border-radius: 15px;
  max-width: 500px;
  overflow: hidden;
}
#display {
  box-sizing: border-box;
  width: 100%;
  padding: 25px;
  font-size: 4.5rem;
  text-align: right;
  border: none;
  background-color: #1f1f2e;
  color: #ffffff;
}

.oprator-btn {
  background: linear-gradient(135deg, #ff7a18, #ff4e00);
  color: white;
  transition: all 0.2s ease;
}

.oprator-btn:hover {
  background: linear-gradient(135deg, #ff9a3c, #ff6a1a);
}

.oprator-btn:active {
  background: linear-gradient(135deg, #e65c00, #cc4400);
  transform: scale(0.95);
}

/* .....< FOR MOBILE FREIENDLY */

@media (max-width: 600px) {
  #calculator {
    width: 95%;
    max-width: none;
    border-radius: 20px;
  }

  #display {
    font-size: 3rem;
    padding: 15px;
  }

  button {
    width: 100%;
    height: 70px;
    font-size: 2rem;
    border-radius: 20px;
  }

  #key {
    gap: 8px;
    padding: 15px;
  }
}