Chromium/Chrome is not perfect as far as gui integration goes but there are a few workarounds.
If you go to Preferences >> Personal, under Appearance you can select "Use GTK theme" and "Use system titlebar and borders".
Now, not always the system titlebar and borders will match chromium's ui (and you use extra space doing this) so I personally use it hidden. I stick to GTK for the icons and colors that match orta.
Equinox (Dawn) seems to have a little issue with the GTK theme as, while it does match and look nice, the icons are that of Faenza-Dark against a light background. You could change those specific icons in the /usr/share/icons/Faenza-dark folder. Not ideal but it works.
The other 3 Equinox gnome themes seem to work fine out of the box with this method.
There are extensions to achieve scrollbars that match your taste/you theme.
Elementary Scrollbar: https://chrome.google.com/webstore/detail/kglninkafjojambbaogionamfcelppil
Elementary Theme: https://chrome.google.com/webstore/detail/pdongokkdiclimbompodchjpdglpfemg )
Simple Bar (Orta-esque scroll):
https://chrome.google.com/webstore/detail/lagmbbmdlgjncefjognkcadapmmkmphe
Adwaita Scrollbar:
https://chrome.google.com/webstore/detail/bkgmaggeefkcgmhmgiadbhgdoeiajccd
There is also a theme for Divergence III (althought Divergence is already at IV).
https://chrome.google.com/webstore/detail/fejliiokfekdkmfjoeggpkdlndgbcopj
And for Shiki:
(White) https://chrome.google.com/webstore/detail/imbkdgihphehomdldnjomialcnehgnih
There are bound to be a few more similars one but my honest advice is to go with GTK if you can't find the specific theme for your setup. :)
Disclaimer: my ubuntu is in portuguese, forgive me if anything is incorrectly named - should be close enough.
