Better wrapping of breadcrumbs when user is logged in

[simonw]

I had this custom CSS on Datasette Cloud:

header p.crumbs {
    padding-right: 2em;
}

Should probably be added to Datasette core, following:

• Add a bit of a gradient to the header and maybe the footer #2302

[simonw]

Here's the difference it makes:

I'm not convinced this is a valuable enough improvement. I'd like to revisit this header at some point in the future, I'll see about improving this then instead.