Since JabRef 5.2 it is possible to use custom themes. In Preferences > Appearance > Visual theme the themes in general can be changed. Themes are just CSS files defining the look of the UI.
Light Theme: The default theme is the light theme (Base.css).
Dark Theme: There is an alternative dark theme (Dark.css) which is based on Base.css and just overwrites the colors.
Custom Theme: In Preferences > Appearance > Visual theme > Custom theme there can be set a custom theme by simply selecting a custom CSS (based on Base.css or Dark.css), for instance:
You can find a collection of user contributed themes at https://themes.jabref.org.
preview box
#previewBody
{} biblatex source tab
.code-area
text in {} biblatex source tab
.code-area .text
#8523: On Windows 10, it is not possible to use fonts that were installed user-wide in the CSS, only system-wide fonts are working. A workaround to use fonts that are not installed system-wide is to include the font file via @font-face.
Light Theme
Dark Theme
Custom Theme (based on the Dark Theme)
