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

body {
    margin: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: hsl(0, 0%, 95%);
}

#calculator {
    font-family: Arial, Helvetica, sans-serif;
    background-color: hsl(0, 0%, 10%);
    border-radius: 15px;
    max-width: 450px;
    overflow: hidden;
}

#display {
    width: 100%;
    padding: 15px 20px;
    color: white;
    font-size: 4rem;
    border: none;
    background-color: hsl(0, 0%, 20%);
}

#display::placeholder {
    color: hsl(0, 0%, 98%);
}

#keys {
    display: flex;
    flex-direction: column;
    padding: 20px;
    gap: 15px;
}

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

button {
    width: 80px;
    height: 80px;
    border: none;
    outline: none;
    border-radius: 50px;
    background-color: hsl(0, 0%, 30%);
    color: #fff;
    font-size: 2rem;
    font-weight: bold;
    cursor: pointer;
}

button:hover {
    background-color: hsla(0, 0%, 40%)
}

button:active {
    background-color: hsl(0, 0%, 70%)
}

.operatorBtn {
    background-color: hsla(36, 98%, 50%)
}

.operatorBtn:hover {
    background-color: hsla(36, 98%, 60%)
}

.operatorBtn:active {
    background-color: hsla(36, 98%, 75%)
}

.actionBtn {
    background-color: hsl(0, 0%, 90%);
    color: hsl(0, 0%, 10%);
}

.actionBtn:hover {
    background-color: hsla(0, 0%, 95%)
}

.actionBtn:active {
    background-color: hsla(0, 0%, 100%)
}