How to change stylesheet ordering of base and child theme?
First of all, if you look into the  section of your code, can you find the css file? If not, it can be that the css is aggregated (in this case you'll find a random alphabetic css file), then clear your cache. If there is no aggregation, and you can't find your file, it is most probably set wrong in your theme.info file.

If the file is there, but not working, check in your browser (via fe element inspect) if and why the selectors are overridden...