Stastic can be installed on an existing website or it allows you to create a new one based on a theme third party website can provide, as explained in the section “[How to install Stastic?]”. You may be feeling like your theme is missing some features or custom design.
Then you have several solutions: 1- Edit your website design on Github, as a standard Jekyll website it will be mostly HTML and CSS work, check out Jekyll docs here. 2- Contact us as explained in the contact page here, and ask for the contact of a Jekyll designer, we will be glad to put you in contact with a freelancer or a company.