The default styles for Activity Plus are pretty bad. In fact, they haven't been changed, or improved since the plugin was released.
The part I'm referring to are the default icons for selecting the image, link, or video input and also the buttons as well. The image buttons are the worst. There are two (add image and cancel) that are unstyled, and one (upload image) that is styled. It is a rather inconsistent look and feel. Not to mention the fact that the icons are still the original ugly ones.
I can accept that they were used in the early releases of the plugin, but that they haven't been updated in the 2+ years the plugin has been in the wild is strange. While I know that I can use my own images for these plugins, I'm tired of having to replace them everytime I setup a new site with Activity Plus. More importantly, shouldn't those icon images be replaced by font icons by now? Automattic's Genericons would be a good set to use.
I know I'm complaining, but I feel like this plugin (which is a great and popular plugin) could use a little love on the look and feel side of things. It wouldn't take much work to change out the default icon images with something better looking (with HiDef/Retina support) and add a few simple CSS rules in the next update.