DOP-5371: update css to match finalized designs

[biancalaube]

Stories/Links:

DOP-5371

Updates:

• active tab selection updated
• Font matching the designs
• static headers updated
• docs home button at top of nav
• update the line seperating the two panels
• view for one only L1s are shown 
• width of the sidenav
• offline snooty button on bottom

should match the double panned designs now

Staging Links:

staging (only loaded the following sites so not all links work: docs-java, docs-c, cloud-docs)

figma

Notes:

• the updated css is just for the double panned nav, not accordion (mobile/tablet) which i will do in another ticket
• dark mode i tried to do but there was no examples in the designs. I reached out to lara but she is on OOO but i will update if needed when she gets back

README updates

• • This PR introduces changes that should be reflected in the README, and I have made those updates.
• • This PR does not introduce changes that should be reflected in the README

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[mmeigs]

Looks so good!

Let's check with design on the width of the Home button! When you hover, the button is as wide as both panels. I'm wondering if it should only be as wide as the main column or some other height specific to it.

[biancalaube]

@mmeigs , thanks for the comments! They should all be addressed now. Reaching out to Lara now to confirm the behavior on hover for the docs home button

[biancalaube]

@mmeigs I fixed the Docs home button hover behavior in DOP-5372, which is the ticket I am working on right now