Though GTK+3 is supposed to take care of scaling fonts with high density
displays, it turns out it is not enough for many, for various reasons (taste,
eyesight, distance to the display…). So we add this additional settings to tweak
further the font size.
With Aryeom, we experimented/discussed both a percentage UI vs. an absolute font
size field (e.g. as they provide in GNOME Tweaks). In the end, we went for a
percentage UI because we realize that we don't necessarily know what is the
current size at all. Mostly you just want bigger or smaller, and don't
necessarily care so much at which value is the font size.
This settings only has a single limitation (that we could find), which is when
used on a theme with widget rules using absolute font-size rules (px, or
keywords such as small/medium/large). As long as the CSS rules are relative
though (either to the parent widget, or to the root size), then it works fine.
Basically a theme hard-coding font sizes won't fare well with this settings, but
since we can consider this bad practice, it's an acceptable limitation.
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