Okay. It looks like it is working now. That is really annoying that Wikia changed the behavior again. Maybe I'll contact them about it.
As for the class, you start by adding it to the element in the page. For example, this is the current state of your "Author's Twitter" header.
<div class="segment-title" style="margin-bottom: 0; text-align:center; font-size:165%; margin-bottom:2px; color:#5EB02E; text-shadow:0 1px 15px #aad9f7; background-image: linear-gradient(to bottom, rgba(255,255,255,0), rgba(255,251,195,0));">'''Author's Twitter{{Icon}}'''</div>
Do you see the class="segment-title"
part? That assigns the class "segment-title" to the div element enclosing the title. You can assign multiple classes to a single element by separating them with spaces. Let's say the new class we want to add is "styled-header". Then we would want this:
<div class="segment-title styled-header" style="margin-bottom: 0; text-align:center; font-size:165%; margin-bottom:2px; color:#5EB02E; text-shadow:0 1px 15px #aad9f7; background-image: linear-gradient(to bottom, rgba(255,255,255,0), rgba(255,251,195,0));">'''Author's Twitter{{Icon}}'''</div>
The second part is adding the proper CSS to your site's CSS. It should look something like this.
.styled-header {
font-family: Righteous, cursive;
}