thread window in side-by-side view is not darkened

[tenmeiiii]

Describe the bug

When opening a thread in side-by-side view, the background image is not darkened.

To Reproduce

Open a thread in side-by-side view

Screenshots

Infomation (please complete the following information)

Discord channel: PTB
OS: Windows 10
Mod: BetterDiscord
Discord language: English

Additional context

I solved it in my own custom css with:

.container-3XgAHv {
  content: "";
  background-position: var(--background-image-position, center);
  background-size: var(--background-image-size, cover);
  background-color: rgba(0, 0, 0, var(--middle-brightness));
}

[Gibbu]

Fixed