Linting the CSS files using the rules proposed in #32888 generates the following violations:

root@df2fd1389bf4:/work# node_modules/.bin/stylelint "public/stylesheets/**/*.css"

public/stylesheets/application.css
  561:1   ✖  Unexpected duplicate selector "div#issue-changesets div.changeset", first used at line 560   no-duplicate-selectors                   
  682:77  ✖  Unexpected duplicate "pre"                                                                   declaration-block-no-duplicate-properties
 1084:1   ✖  Unexpected duplicate selector "table.progress", first used at line 1075                      no-duplicate-selectors                   
 1560:1   ✖  Unexpected duplicate selector ".sort-handle", first used at line 706                         no-duplicate-selectors                   
 1619:83  ✖  Unexpected duplicate "color"                                                                 declaration-block-no-duplicate-properties

public/stylesheets/responsive.css
 264:18  ✖  Unexpected missing generic font family                                                                                                  font-family-no-missing-generic-family-keyword
 804:3   ✖  Unexpected duplicate selector "#issue_tree .issue > td:not(.checkbox), #relations .issue > td:not(.checkbox)", first used at line 787   no-duplicate-selectors                       
 828:3   ✖  Unexpected duplicate selector "#issue_tree .issue > td.subject,   #relations .issue > td.subject", first used at line 799               no-duplicate-selectors                       

public/stylesheets/rtl.css
 322:21  ✖  Unexpected duplicate "margin-right"   declaration-block-no-duplicate-properties
 377:14  ✖  Unexpected empty block                block-no-empty

The attached patches fix all of them with one exception @828:3 ✖ Unexpected duplicate selector "#issue_tree .issue > td.subject, #relations .issue > td.subject", first used at line 799 no-duplicate-selectors@ which should be fixed by #32889.