Describe the bug

Using default theme, nav bar background does not extend fully to the right in widescreen mode, causing customizing with --vp-nav-bg-color to be unusable.

Reproduction

Create a project with default theme with customized CSS:

:root {
    --vp-nav-bg-color: red;
}

Observe that nav bar background does not extend fully to the right in widescreen mode:

Expected behavior

Nav bar background to extend fully.

System Info

System:
    OS: Windows 10 10.0.19045
    CPU: (4) x64 Intel(R) Core(TM) i5-6300HQ CPU @ 2.30GHz
    Memory: 2.24 GB / 11.90 GB
  Binaries:
    Node: 20.18.0 - C:\Program Files\nodejs\node.EXE      
    Yarn: 1.22.4 - ~\AppData\Roaming\npm\yarn.CMD
    npm: 10.8.2 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Chrome: 134.0.6998.166
    Edge: Chromium (127.0.2651.105)
    Internet Explorer: 11.0.19041.4355
  npmPackages:
    vitepress: ^2.0.0-alpha.4 => 2.0.0-alpha.4

Additional context

No response

Validations

• Check if you're on the latest VitePress version.
• Follow our Code of Conduct
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.