/* Reset default styles */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  outline: none;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

/* Full screen container */
body,
html {
  height: 100%;
  background: linear-gradient(to right, #b2dfdb, #80cbc4);
  display: flex;
  justify-content: center;
  align-items: center;
}

/* Main calculator wrapper */
.con {
  width: 100%;
  padding: 20px;
}

/* Calculator box styling */
.cal {
  width: 100%;
  max-width: 320px;
  background-color: #004d40;
  border-radius: 20px;
  box-shadow: 0 0 15px rgba(0, 0, 0, 0.3);
  overflow: hidden;
}

/* Display screen */
.disp {
  width: 100%;
  height: 80px;
  background-color: #263238;
}

.disp input {
  width: 100%;
  height: 100%;
  border: none;
  font-size: 2rem;
  background-color: #263238;
  color: #fff;
  text-align: right;
  padding: 10px;
}

/* Button panel using grid */
.pnl {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
  padding: 15px;
}

/* Buttons */
button {
  background-color: #00796b;
  color: white;
  font-size: 1.2rem;
  font-weight: bold;
  padding: 15px;
  border: none;
  border-radius: 10px;
  box-shadow: 0 4px #004d40;
  transition: all 0.2s;
}

button:hover {
  background-color: #004d40;
  transform: scale(1.05);
}

/* Responsive layout */
@media (max-width: 400px) {
  .cal {
    max-width: 100%;
  }

  button {
    font-size: 1rem;
    padding: 12px;
  }

  .disp input {
    font-size: 1.5rem;
  }
}