.art-btn.art-btn {
    color: var(--btn-primary-txt-colour);
    background-color: var(--btn-primary-bg-colour);
    -webkit-transition: .3s all ease;
    transition: .3s ease all;
    border: none;
    border-radius: var(--radius);
    position: relative;
    z-index: 2;
}
.art-btn.art-btn:before {
    border-radius: var(--radius);
    -webkit-transition: 0.5s all ease;
    transition: 0.5s all ease;
    position: absolute;
    top: 0;
    left: 50%;
    right: 50%;
    bottom: 0;
    opacity: 0;
    content: '';
    background-color: var(--btn-primary-bg-colour-hover);
    z-index: -1;
}
.art-btn.art-btn:hover,
.art-btn.art-btn:focus {
  color: var(--btn-primary-txt-colour-hover);
}
.art-btn.art-btn:hover::before,
.art-btn.art-btn:focus::before {
  -webkit-transition: 0.5s all ease;
  transition: 0.5s all ease;
  left: 0;
  right: 0;
  opacity: 1;
}
.art-btn-group .art-btn.art-btn:not(.art-btn-primary):nth-child(even),
.art-btn-group .art-btn.art-btn.art-btn-secondary {
    color: var(--btn-secondary-txt-colour);
    background-color: var(--btn-secondary-bg-colour); 
}
.art-btn-group .art-btn.art-btn:not(.art-btn-primary):nth-child(even)::before,
.art-btn-group .art-btn.art-btn.art-btn-secondary::before {
    background-color: var(--btn-secondary-bg-colour-hover); 
}
.art-btn-group .art-btn.art-btn:not(.art-btn-primary):nth-child(even):hover,
.art-btn-group .art-btn.art-btn:not(.art-btn-primary):nth-child(even):focus,
.art-btn-group .art-btn.art-btn.art-btn-secondary:hover,
.art-btn-group .art-btn.art-btn.art-btn-secondary:focus {
    color: var(--btn-secondary-txt-colour-hover);
}