.c-collectionbox {
    border: 1px solid #D9D9D9;
    border-radius: 10px;
    padding: 21px;
    width: 3*172px + 2*21px + 2px; 
    font-size: 18px;
    line-height: 24px;
   
    a {
        display: block;
    }
    .c-collectionbox-covers {
        display: flex;
        margin-bottom: 15px;
        img {
            width: 172px;
            @media screen and (max-width: 3*172px + 2*21px + 2px + 2*16px) {
                width: calc((100vw - 2*16px - 2px - 2*21px) / 3);
            }
        }
    }
}