Step 3. Modify your website theme
In order for you to use Site Studio on your existing website, you need to add our cohesion-placeholder tag to your custom theme.
Site Studio uses render placeholders of inline CSS and as these cannot be naturally injected into the HTML template, the site's theme needs to contain <cohesion-placeholder></cohesion-placeholder> within the <head> tag.
To enable Site Studio on a custom theme you must add
cohesion: true to your themes .info.yml file.
After following the above steps and your theme is installed, a Site Studio rebuild is needed to create the required templates.