Ueyen is designed to have smaller selectors, be more customizable, and to reduce the number of required classes for an element to be styled.
You do not need to know how flexbox works in order to use it with Ueyen, if you simply want the items in a flex
container to align on top-right, and you want them to stack as a column, just add the class
un-fl-t-r-co
to your element, the beauty of this is that you do not need to remember the order of "top" indicator
-t, or "right" indicator -r , or column indicator -co. Their order can be
rearranged to anything else, like un-fl-co-r-t, and it still works. Also, this does not mean a heavy
deliverable CSS, the final CSS is very small thanks to the way it distributes the direction values
between selectors. This is also applied to the padding, margin, height and width selectors as well.
Ueyen uses a mapping method for constructing the selectors if you choose to customize the selectors and/or the indicators, you can easily do it with SASS, by downloading the source files.
By using a multiplier system, and custom properties, Ueyen gives you the easiest, breakpoint-ready size manipulation system. All you need to do is to set the multiplier values in the Control Panel, for each breakpoint, and almost all the size-related aspects of the page will become responsive.