Try this CSS:
.wpsp-read-more a.wp-show-posts-read-more {
border-radius: 4px;
box-shadow: 0 12px 20px -10px rgba(0, 0, 0, 0.3);
-webkit-transition: all 500ms ease-in-out !important;
transition: all 500ms ease-in-out !important;
background-color: #20385A;
color: #ffffff;
font-size: 15px;
padding: 15px 20px;
}
.wpsp-read-more a.wp-show-posts-read-more:hover {
background-color: #C6A459;
color: #20385A;
box-shadow: 0 30px 20px -20px rgba(0, 0, 0, 0.3);
-webkit-transform: translate3d(0, -4px, 0);
transform: translate3d(0, -4px, 0);
}