Steps to reproduce:

1. Create a new URP project.
2. Import the extracted contents of the attached Editor.zip.
3. Open Assets > Editor > SimpleCustomEditor.uxml in UI Builder.
4. In the UI Builder, add a new selector to mysheet.uss and add that selector to #button1. Save your changes.
5. Window > UI Toolkit > SimpleCustomEditor.
6. Click the vertical ... menu icon > UI Toolkit Debugger.
7. Click Pick Element in the Debugger, then click on the red button in SimpleCustomEditor.
8. Expand Matching Selectors section.

Actual results: Your new selector's button says mysheet.uss:-1

Expected results: It should be mysheet.uss:12 , or whatever line that new selector is on when you open mysheet.uss in a code editor.

Reproducible with versions: 6000.1.0a4, 6000.0.28f1, 2022.3.52f1, 2022.2.0a17

Can't test with versions: 2021.3, not supported on OS

Tested on (OS): Ubuntu 24.04

Notes:

• Issue is resolved after an editor restart.