body {
    font-family: 'Arial', sans-serif;
    background-color: #f0f2f5;
    margin: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
}

.calculator-container {
    display: flex;
    flex-direction: column;
    align-items: center;
}

.back-link {
    align-self: flex-start;
    margin-bottom: 1rem;
    text-decoration: none;
    color: #007bff;
    font-weight: bold;
}

.calculator {
    background-color: #333;
    padding: 20px;
    border-radius: 15px;
    box-shadow: 0 10px 20px rgba(0,0,0,0.3);
    width: 320px;
}

.display {
    background-color: #222;
    color: white;
    font-size: 2.5rem;
    text-align: right;
    padding: 15px;
    border-radius: 10px;
    margin-bottom: 20px;
    min-height: 50px;
    word-wrap: break-word;
}

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

.btn {
    padding: 20px;
    font-size: 1.2rem;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    background-color: #555;
    color: white;
    transition: background-color 0.1s;
}

.btn:hover {
    background-color: #777;
}

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

.btn-operator:hover {
    background-color: #ffaa33;
}

.btn-equal {
    background-color: #28a745;
    grid-row: span 2;
}

.btn-equal:hover {
    background-color: #34ce57;
}

.btn-clear {
    background-color: #dc3545;
}

.btn-clear:hover {
    background-color: #e4606d;
}

.btn-zero {
    grid-column: span 2;
}