Created attachment 19341 [details]
It seems there is a icon inside the search button. This makes the button look over-sized compared to the search box, and the relation between them became less evident. Removing the image and thereby making the button smaller will also allow for more space for the category list, hence allowing for more categories to be shown at once.
Created attachment 19342 [details]
Proposed button appearence
Agreed, thanks. Fixed in 7686da5550b24b385f9e52209a5d8e5b0bb95a55.