DevTools: fix console dark theme regression
DevTools: fix console dark theme regression

Recently, Console message border colors became CSS variables, which
are preserved in dark theme by default. This CL fixes the regression
by giving explicit dark colors.

Screenshot: https://imgur.com/a/7Hj2GXb

Bug: none
Change-Id: Ib62c8ffa0454303e35699f1d1c70e398a185d52a
Reviewed-on: https://chromium-review.googlesource.com/1159208
Commit-Queue: Erik Luo <26192f5e05d23e5ee959014fb911d780e566545b@chromium.org>
Commit-Queue: Andrey Lushnikov <73889f071ff743ad62763f13ff61c52ca3ee19d0@chromium.org>
Reviewed-by: Andrey Lushnikov <73889f071ff743ad62763f13ff61c52ca3ee19d0@chromium.org>
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#579979}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 09236caff0505fbe95f28d6b07ca391002c360bd
ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,dart-archive/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,dart-archive/devtools-frontend,dart-archive/devtools-frontend,ChromeDevTools/devtools-frontend,dart-archive/devtools-frontend,ChromeDevTools/devtools-frontend