<style>
:root {
    --bg: #000000;
    --color:transparent;
    --hover-color:#000;
}
.button .tn-atom {
    position: relative;
    overflow: hidden;
}

.button .tn-atom:after {
    content: "";
    position: absolute;
    left: 0;
    top: 0;
    width: 56px;
    height: 100%;
    border-radius: 50%;
    background: var(--bg);
    transition: all 0.4s ease;
    z-index: -1;
}

.button .tn-atom:before {
    position: absolute;
    content: "";
    top: 50%;
    left: 1.0625rem;
    width: 10px;
    height: 10px;
    border-top: 2px solid #fff;
    border-right: 2px solid #fff;
    transform: translate(15%, -50%) rotate(45deg);
    transition: all 0.4s ease;
}
.button .tn-atom {
    border-color: var(--color)!important;
}
.button .tn-atom:hover {
    border-color: var(--hover-color);
}
.button .tn-atom:hover:after {
    width: 100%;
    border-radius: 0;
}

.button .tn-atom:hover:before {
    transform: translate(100%, -50%) rotate(45deg);
}
</style>