Steps to replicate the issue (include links if applicable):

• using browser on a Desktop PC
• have HotCat activated
• The following option is activated in "Preferences" > "Gadgets" > "Interface: Files and categories" > "Place categories above all other content. "
• select the "up" or "down" arrow in the HotCat menu for a file's category, to browse available parent or child categories
  • --> problematic files have a long-enough filename to be displayed in two lines instead of one (reduced window sizes also work to wrap title lines)
  • --> problematic files must have a long-enough list (seven or more entries) of selectable parent/child categories
• HotCat offers a drop-down menu that opens either upwards or downwards (depending on how much space is available?)

What happens?:
see attached screenshot below
The upwards-facing drop-down menu exceeds the frame of the application (indicated with the added red line in the screenshot). All offered entries that are entirely out of the frame, above the virtual red line, are not selectable via the mouse cursor. (They are still accessible via the keyboard arrow keys).

In the worst case, the offered category entries are displayed behind the "View"/"Edit"/"History" tabulators.

What should have happened instead?:

Either of the three solutions:

• entries of the drop-down menu should be clickable even outside the frame (probably a bad implementation, this is likely to cause more display bugs in my opinion)
• the gadget should calculate the available space only up to the frame's edge, and open downwards if there is not enough space before reaching the frame/border.
• the gadget should recognize the "place categories above of all other content"-preference, and always offer the downwards facing dropdown menu.

This is likely never an issue with Categories displayed at the bottom of the frame and below the content; and it seems to me that upening the drop-down menu upwards is the default behaviour.

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia): --> Wikimedia Commons

Other information (browser name/version, screenshots, etc.):

Tested in Chrome and Firefox, but likely all browsers.
https://commons.wikimedia.org/wiki/File:HotCat_drop-down-selection_bug.png