style.css

* {
     box-sizing: border-box;
     margin: 0;
}

.calculator {
     background-color: #f2f2f2;
     padding: 20px;
     max-width: 400px;
     margin: 0 auto;
     border: solid 1px #ccc;
     box-shadow: 0 2px 5px rgba(0, 0, 0, 0.3);
     border-radius: 5px;
     margin-top: 40px;
}


#result {
     width: 100%;
     padding: 10px;
     font-size: 24px;
     border: none;
     box-shadow: 0  2px 5px rgba(0, 0, 0, 0.3) inset;
     border-radius: 5px;
}

.buttons {
     display: grid;
     grid-template-columns: repeat(4, 1fr);
     grid-gap: 10px;
     margin-top: 20px;
}

button {
     padding: 10px;
     font-size: 24px;
     border: none;
     box-shadow: 0 2px 5px rgba(0, 0, 0, 0.3);
     border-radius: 5px;
     cursor: pointer;
     transition: background-color 0.3s ease;
}

button:hover {
     background-color: #ddd;
}

.clear {
     background-color: #ff4136;
     color: #fff;
}

.operator {
     background-color: #0074d9;
     color: #fff;
}

.number, .decimal {
     background-color: #fff;
     color: #333;
}

.equals {
     background-color: #01ff70;
     grid-row: span 3;
     color: #fff;
}