Web server: Styles look different with `sg run web-standalone`

Created by: pdubroy

• Sourcegraph version: 8469a104572005c6caffaa9cb69ab38e351fc296
• Platform information: macOS, Chrome Version 90.0.4430.93

Steps to reproduce:

1. Run sg run web-standalone, go to http://localhost:3443/github.com/sourcegraph/sourcegraph/-/blob/client/web/src/site-admin/SiteAdminSurveyResponsesPage.tsx
2. Compare to https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/client/web/src/site-admin/SiteAdminSurveyResponsesPage.tsx

Expected behavior:

Styles look the same.

Actual behavior:

Styles look different.

https://user-images.githubusercontent.com/17293/117460824-34e99d00-af4d-11eb-83dc-4d9c6cbfd245.mp4