body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    font-family: Arial, sans-serif;
    background-color: #f0f0f0;
}

.calculator {
    width: 320px;
    border: 1px solid red;
    border-radius: 10px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
    background-color: #fff;
}

.display {
    padding: 20px;
}

.display input {
    width: 100%;
    border: none;
    background: none;
    text-align: right;
    font-size: 2.5em;
    padding: 0;
    color: #333;
}

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

.btn {
    border: none;
    background-color: #f9f9f9;
    padding: 20px;
    font-size: 1.5em;
    cursor: pointer;
    transition: background-color 0.2s;
}

.btn:hover {
    background-color: #e0e0e0;
}

.btn:active {
    background-color: red;
}

.operator {
    background-color: #f0ad4e;
    color: #fff;
}

.operator:hover {
    background-color: #ec971f;
}

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

.equal:hover {
    background-color: #4cae4c;
}

@media (max-width: 360px) {
    .calculator {
        width: 100%;
        height: 100%;
        border-radius: 0;
    }
}