CSS selectors do work a bit differently. You cant chain class and id selectors that way. In CSS there is prioritized hierarchy and the ID precedes the class. That is what is completely wrong with the syntax.
But also -
You are stepping on the land of kind of restricted area. Group layout is not meant to be changed. Positional properties for groups are set by the dashboard layout logic with inline CSS rules and that has higher priority than id. So your changes don't apply that way anyhow.
The card layout system of dashboard (you like it or not) is something you'll need to respect. There is nothing to fight against. And if this becomes obstacle - you have to create the dashboard from scratch, using for example uibuilder.