body {
  margin: 0;
  height: 100vh;
  font-family: 'Segoe UI', sans-serif;

  /* Background image */
  background: 
    linear-gradient(rgba(255,255,255,0.85), rgba(255,255,255,0.85)),
    url('https://images.pexels.com/photos/5184960/pexels-photo-5184960.jpeg');

  background-size: cover;
  background-position: center;
  background-repeat: no-repeat;

  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
}

/* Heading */
.title {
  color: #333;
  margin-bottom: 20px;
  font-size: 32px;
}

/* Calculator container */
.calculator {
  background: #ffffff;
  padding: 20px;
  border-radius: 25px;
  box-shadow: 0 10px 25px rgba(0,0,0,0.15);
  width: max-content;
}

/* Display */
#display {
  display: block;
  margin: 0 auto 15px auto;
  width: 90%;
  height: 70px;
  font-size: 28px;
  text-align: right;
  padding: 10px;
  border-radius: 15px;
  border: none;
  background: #f5f5f5;
  color: #222; /* dark text instead of white */
}

/* Buttons grid */
.buttons {
  display: grid;
  grid-template-columns: repeat(4, 70px);
  gap: 12px;
  justify-content: center;
}

/* Base button style */
button {
  height: 70px;
  width: 70px;
  border-radius: 50%;
  border: none;
  font-size: 20px;
  cursor: pointer;
  background: #e0e0e0;
  color: #333;
  transition: 0.2s;
}

/* Hover */
button:hover {
  transform: scale(1.08);
  background: #d5d5d5;
}

/* Function buttons */
.function {
  background: #bdbdbd;
  color: #000;
}

/* Operator buttons */
.operator {
  background: #ffb74d;
  color: white;
}

/* Equal button */
.equal {
  background: #ff9800;
  color: white;
  height: 150px;
  border-radius: 35px;
  grid-row: span 2;
}

/* Zero button */
.zero {
  width: 150px;
  border-radius: 35px;
  grid-column: span 2;
}