* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Arial, sans-serif;
    background-color: #f0f0f0;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
}

.calculator {
    background-color: #1c1c1c;
    border-radius: 20px;
    padding: 20px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.3);
    width: 320px;
    max-width: 100%;
}

.display {
    background-color: #1c1c1c;
    color: white;
    font-size: 48px;
    text-align: right;
    padding: 20px;
    margin-bottom: 10px;
    word-wrap: break-word;
    overflow-wrap: break-word;
    min-height: 80px;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 70px);
    gap: 10px;
    justify-content: center;
}

.btn {
    background-color: #333;
    border: none;
    color: white;
    font-size: 24px;
    width: 70px;
    height: 70px;
    border-radius: 50%;
    cursor: pointer;
    transition: background-color 0.2s;
    display: flex;
    align-items: center;
    justify-content: center;
}

.btn:hover {
    opacity: 0.8;
}

.btn:active {
    transform: scale(0.95);
}

.btn.number {
    background-color: #666;
}

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

.btn.function {
    background-color: #a6a6a6;
    color: #000;
}

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

.btn.zero {
    grid-column: span 2;
    border-radius: 35px;
    width: 150px;
}