How to show buttons liink in AMP

hi i use the newspaper themes but the buttons i make link for them doese not have any style i add this to Custom CSS but nothing change

a.wp-block-button__link {
    border-radius: 50px;
    padding-top: 15px;
    padding-right: 36px;
    padding-bottom: 15px;
    padding-left: 36px;
    text-decoration: none;
    color: #fff;
    font-weight: 500;
    background-color: rgb(50, 55, 60);
}

The page I need help with: [log in to see the link]