Management WebUI: Use px instead of em

Bug: 956781
Change-Id: I9b9388cc003b96d8fed93b63bcbd6c2fdbdfa823
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1585240
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Commit-Queue: Yann Dago <ydago@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654283}
1 file changed