ui: Use base fonts throughout the app

[johncowen]

We've had a set of font %placeholders in our base styles for quite a while
but not bitten the bullet to use them. This begins to use them.

We had to make a small amount of tweaks to base whilst doing this, but
its as we'd prefer there to be as few font placeholders as possible. We
might/should be able to reduce these further at somepoint, or
potentially rename them. We currently have six header fonts (or 4 header
fonts/2 strong body fonts) and 3 body fonts.

We also noticed an empty CSS file and deleted that while we were here.
We also noticed that the bottom border of structure tabs was a pixel
larger than ours so we tweaked that here also.

Moving forwards we are likely to make some tweaks to our base files
to bring the 100% into line with structure. Our app typography.scss file
is now much smaller/saner.

Preview link.

Further down the line we are considering moving a lot of this into a
component/component-name/typography.scss file (so similar to the layout.scss/skin.scss files). We've quibbled
about doing this for a while as generally you want fonts to cascade/be
configured from the outside as much as possible and not have the component
itself dictate font sizes. If we do move any of this to the component specific file,
we'll probably make it optional so you still have the option of doing it at a project
level.

[codecov]

Codecov Report

Merging #6881 into ui-staging will decrease coverage by 0.02%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##           ui-staging   #6881      +/-   ##
=============================================
- Coverage       65.63%   65.6%   -0.03%     
=============================================
  Files             443     443              
  Lines           53292   53292              
=============================================
- Hits            34977   34964      -13     
- Misses          14096   14108      +12     
- Partials         4219    4220       +1

Impacted Files	Coverage Δ
agent/router/manager.go	87.5% <0%> (-5.36%)	⬇️
agent/consul/session_ttl.go	85.48% <0%> (-3.23%)	⬇️
agent/consul/replication.go	85.71% <0%> (-2.39%)	⬇️
agent/consul/config_replication.go	75.51% <0%> (-2.05%)	⬇️
agent/kvs_endpoint.go	75.44% <0%> (-1.2%)	⬇️
api/watch/funcs.go	74.61% <0%> (-1.04%)	⬇️
agent/service_manager.go	81.62% <0%> (-0.86%)	⬇️
agent/consul/connect_ca_endpoint.go	56.52% <0%> (-0.67%)	⬇️
agent/consul/leader_connect.go	70.58% <0%> (-0.44%)	⬇️
agent/consul/leader.go	69.61% <0%> (-0.39%)	⬇️
... and 6 more

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[ghost]

Hey there,

This issue has been automatically locked because it is closed and there hasn't been any activity for at least 30 days.

If you are still experiencing problems, or still have questions, feel free to open a new one 👍.