Allow User To Set HTML Element CSS

I have a requirement from a client to add functionality to a MVC/Bootstrap web application to allow the user to design their portal page to fit their company branding colors on form elements such as buttons, links etc. I'm not sure how to implement this. My thought is to save the elements and colors to a db table with a fk to [user]. Then somehow dynamically create a css file and save it to local storage and then inject the user-specific css into the page onload. Any help/guidance would be appreciated.