Fix nav style

[youluna]

当item高度很高的时候，箭头在展开、未展开的情况下位置偏移明显

[codecov]

Codecov Report

Merging #1751 into feat-life-cycle will not change coverage by %.
The diff coverage is n/a.

@@               Coverage Diff                @@
##           feat-life-cycle    #1751   +/-   ##
================================================
  Coverage            90.00%   90.00%           
================================================
  Files                  275      275           
  Lines                15682    15682           
  Branches              5108     5108           
================================================
  Hits                 14115    14115           
  Misses                1540     1540           
  Partials                27       27           

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