Chrome Version: 67.0.3393.4 (Official Build) dev (64-bit)
OS: Linux

What steps will reproduce the problem?
(1)load the attached testcase
(2)
(3)

What is the expected result?
The disclosure triangle should be to the left of the ::before text.
(See Firefox Nightly for correct results.)

What happens instead?
The disclosure triangle is to the right of the ::before text.

I've included a <li> with ::before/::after pseudos for comparison.
I tend to think the <summary> disclosure symbol should render relative
the <summary> ::before in the same way as it is for <li>.
 

Deleted: summary-pseudos.html 538 bytes

summary-pseudos.html 538 bytes View Download