Description:
When launching Steam Big Picture Mode on Windows 11, a small strip of the desktop remains visible along the bottom of the screen. This only happens when the Windows taskbar is set to auto-hide. Big Picture Mode does not fully cover the screen and leaves a thin line of the desktop exposed.

Steps to Reproduce:
On Windows 11, set the taskbar to auto-hide.
Launch Steam normally.
Enter Big Picture Mode.
Observe the bottom of the screen.

Expected Behavior:
Big Picture Mode should occupy the entire screen with no part of the desktop visible, regardless of taskbar auto-hide settings.

Actual Behavior:
A small sliver (thin horizontal line) of the Windows desktop is still visible at the bottom of the screen while in Big Picture Mode.

System Info:
OS: Windows 11
Taskbar setting: Auto-hide enabled

Additional Notes:
Setting the taskbar to “always visible” or “never auto-hide” removes the issue.