My subtheme css is overriden by the parent theme. How to I reverse this?
I'm encountering the same issue.  If I disable the css aggregation I can see that the reason is that my sub-theme's css stylesheet is being @imported before the one(s) from the base theme, which means, of course, that the base theme's styles are overriding mine anywhere where I use the same selectors.  Which is crazy.  How is this not a problem for more people?  Is there something we're missing here?

Edit: sure, I can use !important, which is what I'm doing as a workaround (and presumably the OP @Nigel Waters could do the same?), but doesn't this rather defeat the purpose to some degree?