1. Please paste the custom CSS code to “Appearance > Customize : Additional CSS”:

@media (min-width: 768px) {
.postid-79 .gallery-post-des { margin-bottom: 0px; }
}
@media (max-width: 767px) {
.responsive-ux.postid-79 .gallery-post-des {  margin-bottom: 0px; }
}

note: the CSS will affect only this post, to affect all posts, please remove .postid-79

2. Yes, it is the style of this button link.
If you want to change the style, like to add border, please use the custom CSS:

.gallery-link-a { 
    border: 1px solid currentColor;
    padding: 10px;
}
.gallery-link-a:after: { 
display: none; 
}

Regards!
Bwsm – uiueux.com – Twitter – Facebook