As that is not the phpBB default style then it is either something in the style or some extension that you have installed.
To me it looks like the board header - in fact the whole of your style looks screwed up.
David Remember: You only know what you know and - you don't know what you don't know! My CDB Contributions | How to install an extension I will not be accepting translations for any of my extensions in Github - please post any translations in the appropriate topic. No support requests via PM or email as they will be ignored