Using Eclipse 2020-09 (i.e. v. 4.17) IDE for Java (on Linux, openSUSE Tumbleweed), with version 3.0.38 of Mylyn WikiText plugin installed, I had the following difficulty: Although pretty much all editor/ui fonts were fine, the HTML preview of WikiText files (in particular README.md!) displayed in unreadably small fonts (my display has a very small pixel pitch). So I wanted to find a way to set the CSS of such preview pages. The Mylyn WikiText docs (at https://help.eclipse.org/2020-09/index.jsp?topic=%2Forg.eclipse.mylyn.wikitext.help.ui%2Fhelp%2FMylyn+WikiText+User+Guide.html, under the heading "Rendering Appearance") says that there should be a Preferences screen General > Editors > Text Editor > WikiText > Appearance that allows one to set this CSS. However, no such screen shows up in my installation.
The only method I was able to find for fixing this was to use an application (such as Engrampa) which is able to edit the contents of .jar files, and in my eclipse installation directory, use it on plugins/org.eclipse.mylyn.wikitext.ui_3.0.[SPECIFIC_VERSION_HERE].jar to edit the internal component org/eclipse/mylyn/internal/wikitext/ui/viewer/default.css -- I could change any css there, and upon restarting Eclipse, the changes would take effect.
However, clearly any changes I make this way will be blown away upon the next update of Eclipse or of Mylyn Wikitext. Does anyone know of a better way to set the size of the preview text? Was that Appearance pane mentioned in the docs removed? If so, what replaced it? If not, any ideas why I might not be seeing it?
