Den Customization CSS Question!

I've been putting tons of time into making my Den and User pages looks pretty with CSS and Tetra's CSS Template and Guide, but I've run into a roadblock.

I can't figure out how to change the color of the green boxes containing the "Create a New Cave", "Expand Territory", and "Add Immortal Slot" information. The pre-existing green clashes with my color scheme, and I haven't found a way to fix it yet, so if anyone who has used CSS for their Den has any insights, it would be much appreciated!

The selector for those boxes are:

#main .card {

     // your desired colours here

}

Hope this helps you!