Fix style of sheriff selector on alerts-page.
Fix style of sheriff selector on alerts-page.

https://dev-benjhayden-c99086d7-dot-chromeperf.appspot.com/alerts

https://github.com/catapult-project/catapult/issues/3950
Change-Id: Ic226e99ff83360ba0926777035c9885acb4a6a79
Reviewed-on: https://chromium-review.googlesource.com/706103
Reviewed-by: David Tu <baa605d781958521249fdcf7bad76b01d943134a@chromium.org>
Reviewed-by: Simon Hatch <490a224d89645d3fea983d7189ce51bde0a00c1d@chromium.org>
Commit-Queue: Ben Hayden <d3ffe0e065c2328e497bb32a07f4dcb29138ef5b@chromium.org>

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult