Steps to replicate the issue (include links if applicable):

• Go to https://de.wikivoyage.org/wiki/Portal:Baden-Württemberg/Top-Reiseziele?vectornightmode=1 (is in ns 100)
• All tables use sortable class but the right-hand markers are missing
• Contrary: https://de.wikivoyage.org/wiki/Gouvernements_in_%C3%84gypten is working fine

What happens?:

• No sortable markers are shown

What should have happened instead?:

• Sortable markers have to be shown

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):

The cause is a night mode rule in particular the !important statement:

@media screen {
  .skin-theme-clientpref-night .ns-100 .mw-parser-output :not(.notheme):not(a) {
    background: inherit !important;
  }
}

Please add !important statements to the marker rules like:

html.skin-theme-clientpref-night.client-js .jquery-tablesorter th.headerSort {
  background-image: url(/w/resources/src/jquery.tablesorter.styles/images/sort_both_inverted.svg?d764d) !important;
  background-repeat: no-repeat !important;
  background-position: center right !important;
}