In order to check whether theming works successfully, and if the colour variables are triggering, we should just switch between a couple of themes and see how does the screen behave. Dark+ and Light+ are the two most used themes, however, it's always good to push this to the extreme and try with some extravagant theme like Red. In such extreme conditions we can see, for example, that this toggle switch isn't correctly picking up theme colour as it remains blue (and nothing else in the Red theme UI is actually blue).
Thus we can utilise the previous test of checking if this toggle is actually using variables, and notice this:
The background colour on hover is a hard-coded value rgb(0, 90, 158), instead of an appropriate variable, which would in this case be var(--vscuie-button-hoverBackground);