Google chrome bar highlighting

Does anyone know how to achieve such effect of highlighting the Google chrome interface above the site? google chrome bar highlighted

As you can see the highlight only appears above the site area.

This is the information I gathered:

• It works only in Chrome, highlighting depends on your actual Chrome theme (it changes its color).
• It works on different machines / accounts.
• It works only on that site (at least I haven't encountered such effect on other sites).
• The site is a progressive web app, but its manifest is super simple, there is only gcm_sender_id in it.
• The site has a service worker.