body {
    margin: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: hsl(0, 0%, 15%);
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

#calculator {
    background-color: hsl(0, 0%, 10%);
    border-radius: 20px;
    max-width: 400px;
    overflow: hidden;
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.5);
    padding: 20px;
}

#display {
    width: calc(100% - 40px);
    padding: 20px;
    font-size: 2.5rem;
    text-align: right;
    border: none;
    outline: none;
    background-color: hsl(0, 0%, 20%);
    color: white;
    border-radius: 10px;
    margin-bottom: 20px;
    box-shadow: inset 0 2px 5px rgba(0, 0, 0, 0.3);
}

#keys {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 15px;
    padding: 10px;
}

button {
    width: 100%;
    height: 70px;
    border-radius: 20px;
    border: none;
    background-color: hsl(0, 0%, 25%);
    color: white;
    font-size: 2rem;
    font-weight: bold;
    cursor: pointer;
    transition: background-color 0.2s, transform 0.1s;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.3);
}

button:hover {
    background-color: hsl(0, 0%, 35%);
    transform: scale(1.05);
}

button:active {
    background-color: hsl(0, 0%, 45%);
    transform: scale(0.95);
}

.operator-btn {
    background-color: hsl(35, 100%, 55%);
    color: hsl(0, 0%, 10%);
}

.operator-btn:hover {
    background-color: hsl(35, 100%, 65%);
}

.operator-btn:active {
    background-color: hsl(35, 100%, 75%);
}

#equals-btn {
    grid-column: span 2;
    background-color: hsl(120, 70%, 50%);
    color: white;
}

#equals-btn:hover {
    background-color: hsl(120, 70%, 60%);
}

#equals-btn:active {
    background-color: hsl(120, 70%, 70%);
}

#clear-btn {
    background-color: hsl(0, 70%, 50%);
    color: white;
}

#clear-btn:hover {
    background-color: hsl(0, 70%, 60%);
}

#clear-btn:active {
    background-color: hsl(0, 70%, 70%);
}