Open Radar

 
Summary:
The Full Screen button on windows looks more like a square with a crossout line through it than like two arrows, especially at small sizes/resolution, and especially in its grayscale variation (like in QuickLook).

Even worse is its "Exit Full Screen" rendering, which reads more like a bowtie or some kind of hazmat symbol.

This is partly caused by its "too clever" rendering—trying to fit it into geometric primitives—and partly by it being different in style from the X and — buttons next to it. The glyphs on those buttons are rendered as thin lines, while the Full Screen button uses chunky shapes.

The old + symbol would fit better, or perhaps two chevrons (such as those already used for dropdown menus).

Steps to Reproduce:
Look at the Full Screen button ("< >") on any window that supports it.

Expected Results:
The Full Screen button should clearly communicate its purpose and fit well with other similar controls.

Actual Results:
The Full Screen button does not clearly communicate its purpose. It can be misread in a way that disincentivizes the user from using it. It is also visually inconsistent with the X and — buttons next to it.