body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #f7f7f7;
    margin: 0;
    font-family: 'Roboto', sans-serif;
}

.calculator {
    border-radius: 5px;
    box-shadow: 0px 0px 20px 0px rgba(0, 0, 0, 0.2);
}

.calculator-screen {
    width: 100%;
    height: 80px;
    border: none;
    background-color: #252525;
    color: white;
    text-align: right;
    padding-right: 20px;
    padding-left: 10px;
    font-size: 2.5rem;
}

.calculator-keys {
    width: 100%;
    display: grid;
    grid-template-columns: repeat(4, 1fr);
}

button {
    height: 60px;
    font-size: 1.5rem;
    border: 1px solid #e5e5e5;
    background-color: white;
    color: #333;
    outline: none;
    cursor: pointer;
}

button:hover {
    background-color: #f0f0f0;
}

.operator {
    background-color: #ff9500;
    color: white;
}

.operator:hover {
    background-color: #e08a00;
}

.equal-sign {
    background-color: #ff9500;
    color: white;
    grid-column: span 2;
}

.equal-sign:hover {
    background-color: #e08a00;
}

.all-clear {
    background-color: #ff3b30;
    color: white;
    grid-column: span 2;
}

.all-clear:hover {
    background-color: #e02a2a;
}