UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.12 Safari/537.36

Steps to reproduce the problem:
1. Open https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/checkbox

What is the expected behavior?
In the div labelled "Output", checkboxes next to "Scales", "Horns", "Claws" each. The one next to "Scales" should be checked, the other two unchecked.

What went wrong?
All checkboxes are invisible.

Did this work before? Yes macOS 10.13

Chrome version: 68.0.3440.75  Channel: stable
OS Version: OS X 10.14.0
Flash Version: 

This issue happens on lots of major web sites (github, slack, ...) but not google's (google.com, youtube.com). It does happen in this "New issue wizard", making reporting this bug a challenge.

I can reproduce the bug on Chrome stable (Version 68.0.3440.75) and Chrome beta (same version number  68.0.3440.75 (?)), but not on Chrome dev (Version 69.0.3497.12) (and neither on Canary Version 70.0.3507.0)

According to https://www.chromestatus.com/features/schedule, the Dev Channel will be released on October 16, which might be too late given that the last three macOS updates were published at the end of September.

(Personally, I would even consider this type of bug unacceptable on a beta OS).

Specs:
iMac Pro (2017)
Radeon Pro Vega 56 8176 MB
macOS 10.14 Beta (18A336e)