Indent and Outdent

Solution 1:

You might want to check out the following post: What is the opposite word to "indent"—"outdent" or "unindent"?.

@BoldBen has offered a solid answer, but I'll try the following anyway, recognizing that it's iffy.

It would appear that the hypernym of indentation and outdentation is dentation.

The dictionary definitions of dentation don't apply directly to your situation. However, it would seem that the same logic that gave rise to indentation as you're using it, and that seems to have given rise much more recently, by obvious extension, to outdentation, could be used to justify dentation.

So how about dentation? It could catch on.

Solution 2:

How about Alignment or Text Alignment? You could then include justfication under the same heading if your intention is to reduce the number of headings or button groupings.

If you want to keep justification and indentation separate you could use Indentation since indenting increases the degree of indentation and outdenting decreases it. If your editor will allow outdenting past the left justification of the paragraph, or even into the left margin, you will then create negative indentation, but the concept will still hold.

Margin was suggested above but, for me, margins are part of the page settings rather than aspects of the text. As I said outdenting into the left margin is merely negative indentation.