Yes, there are some tweaks possible, via special style file named
article-style.css.
Try this search to see previous discussions:
http://is.gd/KFpRb7Please note that by default the file doesn't exist in your Goldendict's configuration folder, you have to create it. The config folder location can be obtained via menu: Help -> Configuration folder (assuming you have the Early Access version of Goldendict, not the old released version 1.0.1).