The textarea in the WikiEditor is only vertical resizeable. The textarea in the CodeEditor with disabled code highlighting is vertical and horizontal resizeable. The horizontal resize is not necessary and annoying.

WikiEditor defines in the file modules/ext.wikiEditor.toolbar.styles.less

#wpTextbox1 {
	line-height: 1.5em;
	resize: vertical;
}

This file is in module ext.wikiEditor.toolbar.styles. In WikiEditor loads this module, CodeEditor not.

Is the CSS definition in the right file?
How should the module get loaded?