Tracy panel z-index issues with new theme.

[adrianbj]

I think this shows it pretty clearly. The key thing is that we need the dropdowns to have a higher z-index compared with the top level nav so that Tracy panels can be above the main nav, but below the dropdowns because at the moment you can lose access to the panel's header bar making it hard to move/close.

On the old theme, setting Tracy's panels to 100 worked because the main nav was 0 or 1 (I think) and the dropdowns were 200.

[adrianbj]

Not thoroughly tested, but changing:

#offcanvas-toggle and #pw-mastheads to a z-index of 50 seems to fix the issues with Tracy without breaking the fixed nature of the main nav. Even 99 would be fine. The key thing really is that these are different enough that I can start Tracy panels between one and the other and have enough room for multiple Tracy panels at once (with each one getting a z-index 1 higher than the last).