I've tried to add styles to the Confluence editor. It wouldn't take them. Perhaps one of Atlassian's values is "Don't f@@k the editor".

<web-resource name="editor-scripts" key="editor-scripts">
<resource name="editor-templates.js" type="download"
location="assets/js/editor-templates.js" />
<!-- // TODO: Check whether I need a context here -->

<web-resource name="editor-styles" key="editor-styles">
<resource name="css/confluence-editor.css" type="download"

<!-- // TODO: Check whether I need all the dependencies here --> </web-resource>

My confluence-editor.css styles just wouldn't be accepted. Javascript injection worked just fine though. Perhaps I could use JS to inject my styles?

Yup. Adding this to my editor-templates.js file worked a treat:

var editorCss = AJS.params.staticResourceUrlPrefix
+ '/download/resources/me.davidsimpson.confluence.addon.awesome-addon'
+ ':editor-styles/css/confluence-editor.css';

if (AJS.params.isDevMode) {
editorCss = editorCss + '?_=' + Date.now();

'<link type="text/css" rel="stylesheet" href="' + editorCss + '" media="all">'

Note the cache busting timestamp for local development.