Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 53.69%. Comparing base (fef17a7) to head (d9f5550).

@@            Coverage Diff             @@
##             main    #8685      +/-   ##
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+ Coverage   53.10%   53.69%   +0.58%     
==========================================
  Files         106      106              
  Lines        3544     3589      +45     
  Branches     1023     1033      +10     
==========================================
+ Hits         1882     1927      +45     
  Misses       1406     1406              
  Partials      256      256              

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I do not see anything in the "after" screencast that requires JS changes, that should be possible with pure CSS so no heavy mutation observer is required, no?

@susnux adjusted the PR to use minimal needed JS, also rebased and tests fixed.

what is the difference between this JS implementation and a simple CSS on hover animation?

@susnux the CSS :hover fades the bg of each entry in place. The JS moves that single highlight that slides from the old entry to the new one. That travel between separate elements can’t be done by CSS alone cause a transition can only work on the properties of an element itself but not on siblings.

(Maybe it’s not super obvious on the screencast, especially in the top part where there’s an active element. But there is a background highlight which looks like it travels across the different entries.)