Here are screenshots showing before and after the change with a white video

Deleted: crrev.1004112.before_change.png 14.6 KB

	crrev.1004112.before_change.png 14.6 KB View Download

Deleted: crrev.1004112.after_change.png 16.1 KB

	crrev.1004112.after_change.png 16.1 KB View Download

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/442e46708ff8a813c55df22e7061f0b4396301fc

commit 442e46708ff8a813c55df22e7061f0b4396301fc
Author: Tommy Steimel <steimel@chromium.org>
Date: Tue Apr 10 18:19:18 2018

Add shadow to overlay play button

This CL adds a shadow to the overlay play button so that it's visible
against white backgrounds.

Bug:  831032 
Change-Id: If9af93e25efe8a1e1b3cf802629a15c3e2d0597e
Reviewed-on: https://chromium-review.googlesource.com/1004112
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549594}
[modify] https://crrev.com/442e46708ff8a813c55df22e7061f0b4396301fc/third_party/blink/renderer/modules/media_controls/resources/modernMediaControls.css

Tried checking the issue on chrome versions 67.0.3393.0 and 67.0.3394.0 using Mac 10.13.1 with the below mentioned steps.
1. Launched Chrome
2. Navigated to https://jsfiddle.net/9af830ne/
We observed similar behaviour in both the versions while playing video and pausing it with respect to shadow on play button.

@Tommy Steimel: As we are unable to access the link provided in comment#0 can you please provide us with an other test file which helps us to verify the issue in a better way.

Thanks!