I’ve added settings for now for the slider opacity, they are in the Control Panel under Appearance > Theme Tweaks
The main problem as I see it is, that an empty wiki has by default fixed-fluid mode active and fixed-fluid mode is an advanced mode in comparison to fluid-fixed.
I don’t think fixed-fluid mode is obsolete. It lets users set the layout more precisely, a gap between story-river and sidebar can be accomplished and the sidebar is fluid, which means that, when resizing the browser window, the sidebar resizes and the story-river keeps its width. In fluid-fixed mode, when resizing the browser, the sidebar keeps its width and the story-river resizes.
Also, in fixed-fluid mode the tiddler width can be set, in fluid-fixed mode the tiddler width is 100%.
I don’t think we should do that, again, I think we should make fluid-fixed the default sidebar layout as it’s the easier one and give users the possibility to change to fixed-fluid if they want to.
What I’d like to do is hiding the metrics that don’t have anything to do with fluid-fixed mode if fluid-fixed mode is chosen.