body {
    height: 100vh;
    display: flex;
    justify-content: center;
    flex-direction: column;
    align-items: center;
    background: gray;
}

#emoji {
    font-size: 10rem;
    filter: grayscale(1);
    transition-property: transform ,filter;
    transition-duration: 200ms;
    cursor: pointer;
}

#emoji:hover {
    filter: grayscale(0);
    transform: scale(1.2);
}