fix: polish, use easing gradients

[luwes]

See https://larsenwork.com/easing-gradients/

After:

Before:

[vercel]

@luwes is attempting to deploy a commit to the Mux Team on Vercel.

A member of the Team first needs to authorize it.

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Comments	Updated (UTC)
elements-demo-vanilla	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Mar 15, 2024 10:31pm

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.11%. Comparing base (a3662c7) to head (13d3752).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #885      +/-   ##
==========================================
+ Coverage   82.09%   82.11%   +0.01%     
==========================================
  Files          40       40              
  Lines        8439     8447       +8     
  Branches      462      462              
==========================================
+ Hits         6928     6936       +8     
  Misses       1505     1505              
  Partials        6        6              

Files	Coverage Δ
packages/mux-player/src/themes/gerwig/gerwig.html	100.00% <100.00%> (ø)

[AdamJaggard]

Love this!