[Sidebery] Functional tweaks and recommendations

Been using Sideberry for a couple of days and am really impressed with how its level of customization and performance over Tree Style Tabs. I've configured much of the settings to get to a satisfactory setup but I'm still looking for some improvements (implemented in a way that isn't too distracting or take much valuable screen real estate):

Is it possible to move the bottom buttons up to either where the empty space is to the left the top right X, else to the left of the right side buttons on the panels line? And is it possible to move the "+" button for new tab at the position of the first tab?
Any ideas on how to make tabs with playing audio more obvious? The audio icon next to the favicon is quite subtle. If it's possible to be where the tab's X button is on the right when you hover it it would be more obvious (especially if it's colored).
How to make non-active tabs more white? In Sidebery, I already have "Normal foreground for Tabs" set to #ffffff but it's still fairly more gray compared to Active foreground also set to #ffffff.
Is it possible to toggle between a light/dark theme in particular with a hotkey? Useful when working in natural light where sometimes visibility is a priority.
Sometimes a tab will have a cyan-colored dot on the bottom left--what is that an indicator for and what other indicators are there? I only know configured styles of "unloaded tabs" and "unread tabs".
How to make tab count of folded trees a little more obvious? It's very small on the corner of a tab's favicon. I would be satisfied if it's just larger, else if there's no better way then I guess insert this number between the favicon and the title of the tab?
How to make the colors different shades of gray the same for the address bar, Sidebar, and tabs? I would also like to test whether pure black (excluding borders) looks good enough and improves readability for a dark theme.
Is it possible to add a small X button to close the browser all the way to the right without adding an extra bar? I disabled the tabs bar.

Also interested in any functional CSS tweaks that anyone found improved their workflow.

Much appreciated.

P.S. Might as well ask Sidebery users an unrelated question:

What is the "history service" and is it different than Firefox's implementations? When I grant Sidebery permission to use this, the History button at the buttom says "Nothing..." when I visit different sites. I'm not sure it provides any useful info not found by left-clicking and holding the back button fora webpage. Also, does this tweak to highlight opened bookmarks work? I add it to the Sidebery style editor and open a link from bookmark but there's no indicator that it's opened as a bookmark.