I used the gnome tweaks tool to increase the font size to a more comfortable level, but those icons are minuscule. From my research there may be a css setting in the gnome-theme, but I can't find anything that might control the icon size in the window title bar. 

I tried scaling the display in Settings, but 100% is too small without increasing the font size, and 125% is too big. The display scaling does increase the size of the icons, however.

I just notices that Chrome has the icons correctly sized for the font in the window title bar. Weird.

Thanks!

Mark