fix(Theme): fix slow app when the theme is changed

[lukicenturi]

Closes #(issue_number)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 4.16667% with 23 lines in your changes missing coverage. Please review.

Project coverage is 67.76%. Comparing base (e1c8b58) to head (c31931e).

Files	Patch %	Lines
src/composables/theme.ts	4.16%	23 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #208   +/-   ##
=======================================
  Coverage   67.76%   67.76%           
=======================================
  Files         105      105           
  Lines       18738    18737    -1     
  Branches      694      694           
=======================================
  Hits        12697    12697           
+ Misses       6041     6040    -1     

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[kelsos]

lgtm thanks :)