@import url('https://fonts.googleapis.com/css2?family=Poppins:wght@300;400;500;600&display=swap');

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

body {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 100vh;
  background: #0d0d0d;
  padding: 20px;
}

.container {
  border-radius: 15px;
  padding: 20px;
  background: #161616;
  box-shadow: 0 5px 15px rgba(0, 0, 0, 0.6);
  width: 100%;
  max-width: 400px;
}

input {
  width: 100%;
  border: none;
  border-radius: 12px;
  padding: 15px;
  text-align: right;
  font-size: 2rem;
  background: #222;
  color: #00e1ff;
  outline: none;
  box-shadow: inset 0 0 8px rgba(0, 255, 255, 0.2);
  margin-bottom: 15px;
}

input::placeholder {
  color: rgba(0, 225, 255, 0.6);
}

.button-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

/* All Buttons */
button {
  width: 100%;
  padding: 15px;
  border: none;
  border-radius: 15px;
  background: #333;
  font-size: 1.5rem;
  color: white;
  cursor: pointer;
  transition: 0.3s ease-in-out;
  box-shadow: 0 3px 10px rgba(0, 0, 0, 0.3);
}

button:hover {
  background: #00e1ff;
  color: #161616;
  box-shadow: 0 0 15px rgba(0, 225, 255, 0.8);
}

/* Operator Buttons */
.op {
  background: linear-gradient(to bottom, #0077ff, #00c3ff);
  box-shadow: 0 0 8px rgba(0, 195, 255, 0.6);
}

.op:hover {
  background: #00aaff;
  box-shadow: 0 0 12px rgba(0, 195, 255, 0.8);
}

/* Equal Button */
.equal {
  background: linear-gradient(to bottom, #009688, #00ffcc);
  box-shadow: 0 0 8px rgba(0, 255, 204, 0.6);
}

.equal:hover {
  background: #00d9a3;
  box-shadow: 0 0 12px rgba(0, 255, 204, 0.8);
}

/* Responsive */
@media (max-width: 480px) {
  .container {
    padding: 15px;
  }

  input {
    font-size: 1.6rem;
    padding: 12px;
  }

  button {
    font-size: 1.2rem;
    padding: 12px;
  }

  .button-grid {
    gap: 8px;
  }
}