Unstyled black area at the bottom of the login page when system dark theme is enabled

Description:

On the login page ("Welcome back." / SSO screen), a large unstyled black area appears below the login card when the OS-level dark theme is enabled. The rest of the page (header, login card) stays in light theme, but the background below the card renders as solid black, breaking the visual layout.

Steps to reproduce:

Enable dark theme at the operating system level (Windows/macOS/Linux)
Open the Temporal UI login page
Observe the area below the "Continue to SSO" card

Expected behavior:

The entire page should consistently follow the same theme (light or dark), with no unstyled black area.

Actual behavior:

The top of the page stays in light theme (white/light gray background), while the bottom of the page turns fully black, as if some component/container isn't correctly inheriting styles from either the light or dark theme.

Screenshot:

Environment:

System theme: dark
Browser: Microsoft Edge / Google Chrome / Firefox / ...
Temporal UI version: v2.53.3

Start by reproducing the Temporal UI login page with the operating system dark theme enabled, then inspect the page around the “Continue to SSO” card for the container or background that renders black. Verify the fix in Edge, Chrome, or Firefox and confirm the full page remains consistently themed without the unstyled area.