Can't Customize Slide-In Colors & "Close" tab design broken...

Page to reference where I have the test running:

I've managed to get it up and running (It wasn't liking the widget insertion, BTW, but putting code directly in worked). However, there are a couple of issues:

1) there is additional space at the bottom of the slide-in, as well as the "close" tab has been pushed up, making it not very pretty visually.

2) I want to alter the background color of the slide-in... right now option is black or white. I can do this in chrome by inspecting the css and altering it to look (as attached). However, when I paste the css into "custom css" in global settings, it's not having any effect.
Here's the post I've put this into for testing:
Here's the code I'm posting in the Custom CSS:
.wdsi-slide-rounded-dark .wdsi-slide-wrap {
background: #FFA500;
color: #e6e6e6;

Perhaps allowing users to enter RGB/Hex colors for variation (background) and scheme (outline)?

3) I'd like to set a minimum width (770px), so that the slide doesn't scale narrower than the contents (a signup form). Setting message width apparently only sets maximum, not minimum... Maybe an option to set both/either?

If there's just a generally better way to do what I'm trying to do, please advise. Thanks!!