app/assets/stylesheets/base/placeholders.scss
%custom-links {
box-shadow: inset 0 -1px 0 $color-green-rgba-first;
font-weight: lighter;
-webkit-transition: box-shadow .3s ease-in-out;
-o-transition: box-shadow .3s ease-in-out;
transition: box-shadow .3s ease-in-out;
&:hover {
box-shadow: inset 0 -25px 0 $color-green-rgba-second;
text-decoration: none;
}
}