Trouble styling the Edit-mode Textarea element by CSS

[Brian Radspinner]

I'm trying to get colors specified via just CSS to keep everything consistent with CSS variables. I cannot figure out how to change the color of the main text input box in edit mode with CSS instead of a custom palette. It seems like at least one of the below selectors should work...but they do nothing to change the default light-grey background and black text. Any ideas?

.tc-tiddler-frame iframe.tc-edit-texteditor,
.tc-tiddler-frame iframe.tc-edit-texteditor html,
.tc-tiddler-frame iframe.tc-edit-texteditor html body,
.tc-tiddler-frame iframe.tc-edit-texteditor html body textarea,
.tc-tiddler-frame iframe.tc-edit-texteditor-body,
.tc-tiddler-frame iframe.tc-edit-texteditor-body html,
.tc-tiddler-frame iframe.tc-edit-texteditor-body html body,
.tc-tiddler-frame iframe.tc-edit-texteditor-body html body textarea {
    background-color: #fff !important;
   color: #900 !important;
   -webkit-appearance: none;
}