The trick to Webflow CSS is understanding what is happening when you create a global class vs a combo class.
If you want to keep things global then never make changes to the class while it is linked to another. As soon as you make changes to the settings of the nest has a whole Webflow will create a new combo class in the CSS.
What you are running into is not a cascading problem but a specificity problem in CSS. A combo class is more specific then stacked global classes.
I'll explain further with more an example. ( I have pre made the global classes so the settings take effect immediately.)
I start with some basic elements on the page. Similar to my last example I want to create a modular column layout. I know I am going to want to use my classes in many different areas so I create them as Global classes on separate elements.
I start by creating col-20, col-50 and col-80.
Now I want to add some background colour to each column, using a global class.
Everything looks a little close together. I will use my margin and padding global class to give everything uniform spacing.
I am not happy with the background color so I am going to change it. The important thing to remember is you have to select the global class within the nest. If you don't you will create a combo class in the CSS, which will cause you specificity issues.
Does that give you any answers?