HTMLify

body {
    width: 100vw;
    height: 100vh;
    display: grid;
    background: #1e1e24;
    place-items: center;
}

.btn-flip {
    opacity: 1;
    outline: 0;
    color: #fff;
    line-height: 40px;
    position: relative;
    text-align: center;
    letter-spacing: 1px;
    display: inline-block;
    text-decoration: none;
    font-family: "Open Sans";
    text-transform: uppercase;
}

.btn-flip::before,
.btn-flip:after {
    top: 0;
    left: 0;
    transition: 0.5s;
    display: block;
}

.btn-flip::before {
    content: attr(data-front);
    position: relative;
    opacity: 1;
    color: #1e1e24;
    padding: 0 30px;
    line-height: 40px;
    background: #00ffe7;
    transform: translateY(0) rotateX(0);
}

.btn-flip::after {
    content: attr(data-back);
    position: absolute;
    opacity: 0;
    width: 100%;
    color: #000;
    transition: 0.5s;
    background: #e5b4ff;
    transform: translateY(-50%) rotateX(90deg);
}

.btn-flip:hover::before {
    opacity: 0;
    transform: translateY(50%) rotateX(90deg);
}

.btn-flip:hover::after {
    opacity: 1;
    transform: translateY(0) rotateX(0);
}