Referring the above comments and taking pointers from #9, #13 and #16, the following patch makes toolbar fixed across all screen sizes and browsers. Please refer the screenshot attached...
With this patch,
# isFixed and isViewportOverflowConstrained occurrences from JS has been removed.
# Narrow devices will have a fixed top admin toolbar and an overlapping secondary side toolbar.
# Standard devices with side secondary toolbar will push the main content to the right (no overlapping secondary side toolbar), which is the default behaviour as usual (left undisturbed)
# The toolbar-fixed has been permanently added to the toolbar. It is not removed from the code, just in case if it might find some use or other options to compete with in the future.
I have tested across all major browsers and OS simulations and attaching now a couple of screenshots..
Before Patch:
After Patch: