body {
    margin: 0;
    padding: 0;
    background-color: aliceblue;
    font-family: 'Franklin Gothic Medium', 'Arial Narrow', Arial, sans-serif;
    display: flex;
    align-items: center;
    justify-content: center;
    height: 100vh;
}

.theme-toggle {
    position: absolute;
    top: 20px;
    right: 20px;
    background: #fff;
    border: none;
    border-radius: 50%;
    width: 40px;
    height: 40px;
    cursor: pointer;
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.2);
    font-size: 1.2rem;
}

.calculator {
    background-color: #000;
    border-radius: 20px;
    padding: 20px;
    width: 320px;
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.3);
    position: relative;
}

.calculator.light {
    background: #f9f9f9;
}

.display {
    background: #000;
    color: #fff;
    text-align: right;
    padding: 20px 10px;
    border-radius: 10px;
    margin-bottom: 20px;
    font-size: 2rem;
    min-height: 40px;
}

.calculator.light .display {
    background: #fff;
    color: #000;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 15px;
}

button {
    width: 70px;
    height: 70px;
    border: none;
    border-radius: 50%;
    font-size: 1.5rem;
    color: #fff;
    background: #222;
    transition: background 0.2s ease;
    display: flex;
    align-items: center;
    justify-content: center;
}

button:hover {
    background-color: #555;
}

.calculator.light button {
    background-color: #e0e0e0;
    color: #000;
}
.calculator.light button:hover {
    background-color: #ccc;
}

.operator {
    background-color: #f90;
    color: #fff;
}
.operator:hover {
    background: #e68a00;
}

.blue {
    background-color: #2196f3;
    color: #fff;
}
.blue:hover {
    background-color: #1565c0;
}

.zero {
    grid-column: span 2;
    width: 100%;
    border-radius: 35px;
    justify-self: stretch;
}