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

.container {
  background: #e3f9ff;
  width: 100%;
  height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
}

.calculator {
  background: #3a4452;
  padding: 20px;
  border-radius: 10px;
}

.calculator form input {
  border: 0;
  outline: 0;
  width: 60px;
  height: 60px;
  border-radius: 10px;
  box-shadow:
    -8px -8px 15px rgba(255, 255, 255, 0.1),
    5px 5px 15px rgba(0, 0, 0, 0.2);
  font-size: 20px;
  background: transparent;
  color: #fff;
  cursor: pointer;
  margin: 10px;
}

form .display {
  display: flex;
  justify-content: flex-end;
  margin: 20px 0;
}

form .display input {
  text-align: right;
  flex: 1;
  font-size: 45px;
  box-shadow: none;
}

form input.equal {
  width: 145px;
}

form input.operator {
  color: #33ffd8;
}

.calculator form input:hover {
  background: #444e5c;
}

.back-btn {
  position: fixed;
  top: 20px;
  right: 20px;

  padding: 10px 16px;
  background: linear-gradient(135deg, #4f46e5, #6366f1);
  color: #fff;

  font-size: 10px;
  font-weight: 600;
  text-decoration: none;

  border-radius: 8px;
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.15);

  transition: all 0.3s ease;
  z-index: 1000;

  top: 15px;
  right: 15px;
}

.back-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 14px rgba(0, 0, 0, 0.2);
  background: linear-gradient(135deg, #4338ca, #4f46e5);
}

@media (max-width: 360px) {
  .calculator form input {
    width: 52px;
  }

  form input.equal {
    width: 130px;
  }
}