Border bottom, hover full background#
.btn {
text-decoration: none;
display: inline-block;
position: relative;
padding: 6px;
color: rgb(68,68,68);
font-weight: 500;
font-size: initial;
text-transform: initial;
z-index: 1;
}
.btn:before {
content: '';
position: absolute;
bottom: 0;
left: 0;
height: 1px;
background-color: rgb(245,160,7);
width: 100%;
z-index: -1;
}
.btn:hover:before {
height: 100%;
}
.btn:hover {
color: white;
}