Can I use my own theme with Acquia Cohesion?
Yes. You can use your own theme with Acquia Cohesion. There are some additions to your theme required.
You can use Acquia Cohesion with your own custom theme. You need to add the <cohesion-placeholder></cohesion-placeholder> tag within the <head> tag of your theme and
cohesion: true should be set in the themes info.yml file. Find out more about modifying your website theme.