`pane-header` doesn't respond to dark theme

### Jenkins and plugins versions report

ci.jenkins.io, plugin version 574.va_19f05d54df5

### What Operating System are you using (both controller, and any agents involved in the problem)?

N/A

### Reproduction steps

Take a look at a table using `pane-header`, e.g. used by the matrix auth plugin in yourJenkins/manage/configureSecurity/ and notice it's not colored.

### Expected Results

The panes are colored as intended.

### Actual Results

### Anything else?

_No response_

### Are you interested in contributing a fix?

_No response_