This is me probably missing the utterly obvious, which is something I do.

I'd like to increase the font size of the "<<Prev", "Next>>" and "Close X" navigation links in the overlay to the same size as the "Image X of X" but am not seeing where that is set in either options or in CSS (unfortunately inspecting elements with the Web Dev Toolbar does not work with the overlay).

Any guidance on where I might be able to increase font-size of those ellements would be much appreciated.

The text on the English version of the control buttons is part of the background image for those controls (which are actually anchor elements). So to make the text larger, you have to draw your own custom control graphics and modify the css to use those new images. If the background images are of different size than the originals, the sizing in the css will need to be adjusted as per the comments in the css file. Sorry, no quick "font-size=" setting for these.

Makes perfect sense. Thanks for the guidance