Revert "Updates the bottom border to be 15% black instead of black."

This reverts commit f3a6c253c7ae2eb42dd58de281587dbf110ef493.

Reason for revert: suspected for https://bugs.chromium.org/p/chromium/issues/detail?id=923894#c14

Original change's description:
> Updates the bottom border to be 15% black instead of black.
> 
> This is a UX issue that came up during https://crbug.com/918788
> 
> Bug: 853593
> Change-Id: If0efdba2d344ee379fb560c61dc43ea4a14c0510
> Reviewed-on: https://chromium-review.googlesource.com/c/1415232
> Commit-Queue: Jay Harris <harrisjay@chromium.org>
> Reviewed-by: Bret Sepulveda <bsep@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#624515}

TBR=bsep@chromium.org,harrisjay@chromium.org

Change-Id: I7ff365b2fcfafdbd75f6bd506c56f07ab806579d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 853593, 923894
Reviewed-on: https://chromium-review.googlesource.com/c/1425997
Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624635}
1 file changed