Locally I have setup two themes.
Theme Directories app/design/frontend/VendorParent/default //Inherits from Luma app/design/frontend/VendorChild/default //Inherits from VendorParent
On the admin side under Content -> Configuration, I have two websites setup.
Main Website //Uses VendorParent theme Another Website //User VendorChild theme
Under my etc/hosts file I have added entries for both of these sites. I have also added these to the apache vhost file and pointed them both to the same location (magento folder)
127.0.0.1 mainsite.magento.dev 127.0.0.1 anothersite.magento.dev
I went under stores -> configuration -> general -> web. Here I turned off the 'Auto-redirect to Base URL' option for the default site. Then I went into the same place for the anothersite and changed the 'Base URL' and 'Base Link URL' to be anothersite.magento.dev (I also did this for secure urls here).
I can hit both urls properly, however when I go to anothersite.magento.dev, it is trying to load css files for the mainsite.magento.dev, and I am getting a bunch of font CORS errors in the console. here are the paths it is trying to load for the css.
mainsite.magento.com/pub/static/version1498747501/frontend/Main/default/en_US/mage mainsite.magento.com/pub/static/version1498747501/frontend/Main/default/en_US/css mainsite.magento.com/pub/static/version1498747501/frontend/Main/default/en_US/Main/css mainsite.magento.com/pub/static/version1498747501/frontend/Main/default/en_US/css mainsite.magento.com/pub/media mainsite.magento.com/pub/static/version1498747501/frontend/Main/default/en_US/css
And here are the font CORS error paths.
Access to Font at 'http://mainsite.magento.dev/pub/static/version1498747501/frontend/Main/default/en_US/fonts/Blank-Theme-Icons/Blank-Theme-Icons.woff2' from origin 'http://anothersite.magento.dev' has been blocked by CORS policy Access to Font at 'http://mainsite.magento.dev/pub/static/version1498747501/frontend/Main/default/en_US/fonts/Another/Another-Regular.woff' from origin 'http://anothersite.magento.dev' has been blocked by CORS policy: Access to Font at 'http://mainsite.magento.dev/pub/static/version1498747501/frontend/Main/default/en_US/fonts/Blank-Theme-Icons/Blank-Theme-Icons.woff' from origin 'http://anothersite.magento.dev' has been blocked by CORS policy: Access to Font at 'http://mainsite.magento.dev/pub/static/version1498747501/frontend/Main/default/en_US/fonts/Another/Another-Regular.ttf' from origin 'http://anothersite.magento.dev' has been blocked by CORS policy:
Actually now that I look at it, it is using the mainsite url for all assets being loaded on the anothersite url.