Browser: Any
OS: Any
If you select a variable for the value of any style setting (e.g. padding), save the page, open the variable manager, make sure the All category is selected and then filter to show variables used on the page, that variable is shown.
Now remove that variable from the element, create a new class, add the variable again within the class, save and then try and filter to show variables used on the page, the variable is not shown. All variables used in classes are not found by the variable manager’s used on page filter. This basically renders the filter useless as most styling is done in custom classes and therefore we have to look in every class on the page to see if a variable is being used.