Starred emails indication

To make the text italic for starred messages, add this to userChrome.css:

/* italics for starred */
tr[is="thread-card"][data-properties~="flagged"] .sender{
  font-style: italic !important;
}

tr[is="thread-row"][data-properties~="flagged"]{
  font-style: italic !important;
}

The first part makes the sender italic in Cards View, while the second makes the message list header italic in Table View.

Help/Troubleshooting Info, Profile Folder, Open Directory (Win:Folder), close TB, create a new folder named chrome, create a new document in chrome with a text editor, name it userChrome.css, Save as type: All files *.*, copy in the above code. Double-click toolkit.legacyUserProfileCustomizations.stylesheets to true in Settings/General/Config. editor, restart TB.

Online css generator

video: How to create a css file (Firefox or TB)

I opened the "Profile directory" (which was called "/home/j/.thunderbird/2m0gjpw5.default-esr/" in my case, can that be?🤷) Created a file called "userChrome.css" 👍 and pasted the styles closed and reopend thunderbird but nothing really happened👎.

In the devtools I see the <td> flashing when I (un)star an email but no data- or classes added.

Did you toggle the Config. editor setting? Did you place the css file in the chrome subfolder of the profile? The code works here on W11.