body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    background-color: #f0f2f5;
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

.calculator-container {
    text-align: center;
}

h1 {
    color: #333;
}

.calculator {
    width: 340px;
    border-radius: 12px;
    box-shadow: 0 8px 25px rgba(0, 0, 0, 0.15);
    overflow: hidden;
}

.display {
    background-color: #222;
    color: #fff;
    font-size: 2.8em;
    padding: 25px 20px;
    text-align: right;
    word-wrap: break-word;
    word-break: break-all;
}

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

.btn {
    padding: 22px;
    font-size: 1.6em;
    border: 1px solid #ddd;
    cursor: pointer;
    background-color: #fafafa;
    transition: background-color 0.2s ease;
}

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

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

.operator:hover {
    background-color: #e08500;
}

.equals {
    grid-row: span 2;
    background-color: #34c759;
    color: white;
}

.equals:hover {
    background-color: #2da349;
}

.zero {
    grid-column: span 2;
}