*
{
    margin: 0;
    padding: 0;

    box-sizing: border-box;

    font-family: sans-serif;
}

body
{
    display: flex;
    flex-direction: column;

    justify-content: space-between;

    width: 500px;
    height: 60vh;

    margin: 0 auto;

    padding: 10px;

    background-color: #444;
    color: white;
}

a
{
    flex: 0 0 50px;

    padding: 10px;

    text-align: center;

    text-decoration: none;
    color: white;

    background: linear-gradient(#c5c5c5, #636363) 0px 0px / 400% 400% no-repeat;

    border-radius: 3px;

    box-shadow: 0 5px 10px -5px rgba(0, 0, 0, 0.5);

    transition: font-size 100ms ease-in-out, background-position 100ms ease-in-out;
}

a:hover
{
    color: rgb(255, 255, 255);

    font-size: 1.2em;

    background-position: 100% 100%;
}