* {
    box-sizing: border-box;
    font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

body {
    margin: 0;
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    background: #121212;
}

main {
    background: #1e1e1e;
    padding: 20px;
    border-radius: 12px;
    width: 320px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.5);
}

#display {
    background: #000;
    color: rgb(133, 216, 133);
    font-size: 2rem;
    padding: 15px;
    text-align: right;
    border-radius: 8px;
    margin-bottom: 15px;
    overflow-x: auto;
}

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

button {
    padding: 15px;
    font-size: 1.1rem;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    background: #2a2a2a;
    color: #fff;
    transition: background 0.15s ease, transform 0.05s ease;
}

button:hover {
    background: #3a3a3a;
}

button:active {
    transform: scale(0.97);
}

.operator {
    background: #ff9500;
    color: #000;
}

.operator:hover {
    background: #ffb347;
}

#equals {
    background: #00c853;
    color: #000;
}

#equals:hover {
    background: #1de9b6;
}

#decimal {
    background: #444;
}

#clear {
    grid-column: span 4;
    background: #d32f2f;
}

#clear:hover {
    background: #ef5350;
}