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

body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #e0e0e0;
}

.calculator {
    width: auto;
    background-color: #2e2e2e;
    border-radius: 20px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
    padding: 20px;
}

.display {
    background-color: #1a1a1a;
    color: #fff;
    font-size: 2.5rem;
    text-align: right;
    padding: 20px;
    margin-bottom: 20px;
    border-radius: 15px;
    box-shadow: inset 0 5px 10px rgba(0, 0, 0, 0.3);
}

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

button {
    padding: 20px;
    font-size: 1.5rem;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    transition: transform 0.2s;
}

button:hover {
    transform: scale(1.05);
}

.btn {
    background-color: #3d3d3d;
    color: #fff;
}

.btn.clear {
    background-color: #d9534f;
}

.btn.delete {
    background-color: #f0ad4e;
}

.btn.operator {
    background-color: #0275d8;
}

.btn.number {
    background-color: #5bc0de;
}

.btn.equal {
    background-color: #5cb85c;
    grid-column: span 2;
}

button:active {
    background-color: #444;
}