Using Your Own Domain
You can use your own domain with CT on the Premium Plan. This will update your dashboard URL completely.
Please note, due to the limitations with SSL and securing the dashboard, you will be required to use a service such as Cloudflare to 'spoof' the certificate. You can read about this here:
To add a cname, visit your profile > branding.
At the bottom is an option to update your CNAME: