Peek transparency doesn't work well

[robertohuertasm]

Describe the bug
Whenever I open a peek, it doesn't matter dark or light mode, the header is transparent making it very difficult to read.

To Reproduce
Steps to reproduce the behavior:

1. Open a peek by looking for references anywhere in your code.

Expected behavior
The header shouldn't be transparent.

Screenshots
By default:

How I would like to see it:

Additional context

If I disable the background-color property from this class. It works as expected.

Note that this affects ALL THEMES.

[robertohuertasm]

For what I see this is caused because I use sticky scroll in the peek. Ideally, it would be nice to fix the --vscode-peekViewEditorStickyScroll-background value so it wouldn't be transparent.

For now, my workaround is to set the previewEditor.background color to a color that works well with the selected theme. That will affect both the sticky header and the background. Not ideal, but it works:

 "workbench.colorCustomizations": {
    "[Material Theme Darker]": {
      "peekViewEditor.background": "#282727"
    }
  }