button{
    outline: none;
    cursor: pointer;
    display: block;
    overflow: hidden;
    position: relative;
    text-align: center;
    padding: 1em 2.5em;
    border: none;
    color: #4de7d7;
    background-color: transparent;
    font-family: sans-serif;
    font-size: 16px;
    line-height: 1;
    transition: all .2s ease;
    box-shadow: 
        0.3em 0.3em 0 0 #4de7d7,
        inset 0.3em 0.3em 0 0
}

button:hover,
button:focus{
    box-shadow: 0 0 0 0 #4de7d7,
    inset 6em 3.5em 0 0 #4de7d7;
    color: #000;
}