On 2.9.x trying to upload a file on a new style page results in a "no file selected" error message. The same works in 2.10.x
On both 2.9.x and 2.10.x the "upload" links disappears when the page edits an existing style (but not the file upload chooser) making it impossible to update a style by upload.
Both actions work fine in a 2.8.x. I'd guess it's related to the wicket upgrade, although making the "upload" link disappear almost seems like a conscious choice.