After looking into the CSS, it seems that the wiki admin BluesDriver is talking about is very astute. I have managed to find the offending CSS which comes from skin.fandomdesktop.styles. The following copy of the CSS has intermediate lines removed for brevity.
@media screen {
figure[typeof~='mw:File/Thumb'],
figure[typeof~='mw:File/Frame'] {
border: 1px solid #ccc;
border-bottom: 0;
background-color: #f9f9f9
}
figure[typeof~='mw:File/Thumb'] > figcaption,
figure[typeof~='mw:File/Frame'] > figcaption {
border: 1px solid #ccc;
border-top: 0;
background-color: #f9f9f9;
font-size: 88.40000000000001%
}
}
@media print {
figure[typeof~='mw:File/Thumb'],
figure[typeof~='mw:File/Frame'] {
border: 1pt;
border-bottom: 0;
background-color: #fff
}
figure[typeof~='mw:File/Thumb'] > figcaption,
figure[typeof~='mw:File/Frame'] > figcaption {
background-color: #fff;
color: #666;
font-size: 10pt;
border: 1pt;
border-top: 0
}
}
I also noticed that there are some CSS rules that don't have any properties in them; they are just empty. So that suggests to me that Fandom either hasn't finished their revisions of the CSS or they were just sloppy in cleaning up.