Hi! I understand you're having trouble with the font size change boxes in the BorrowBox app not working when you tap them. Just to make sure I get it right, is this issue happening only within BorrowBox while reading eBooks? And is it for all eBooks or certain ones?

In the meantime, I can guide you through some steps that might help:

1. Check if the book uses 'fixed layout': Some eBooks in BorrowBox use what's called a 'fixed layout,' and their font size cannot be changed directly in the app. Instead, you can pinch-to-zoom or use the device’s magnification feature to enlarge the text.

2. Restart the app: Close the BorrowBox app completely and then reopen it. Sometimes this refreshes controls like font size sliders.

3. Update the app: Make sure you have the latest version of BorrowBox installed. Older versions might have bugs affecting font settings.

4. Try adjusting font size in the reading view: When reading a book, tap the center of the screen to bring up the reading menu, and check if the font size slider there responds.

5. Use device zoom options: Since you mentioned using Windows with WebKit, you can also try adjusting the zoom level of your device/browser by pressing Ctrl and + together to zoom in (or Ctrl and - to zoom out). This sometimes helps with non-responsive font controls in apps running on browsers or WebKit.

If none of these steps make the font size box responsive, could you tell me which device you are using? For instance, is this the BorrowBox app on a PC browser, a tablet, or another device? Also, does tapping other controls in the app work fine?

This will help me pinpoint the issue better and provide more precise help!