All the pages in my pure MVC website have Bootstrap's (3 column, footer, header) page template. When I go to Design --> Page Template and select this Bootstrap template, the top right corner has a button called "Themes". When I click that I see a dropdown which allow me to select a theme. Currently, there is only Basic theme option in the dropdown and I want to use a custom theme for this template which will be selectable from this dropdown.
I am totally stuck as to how to go about to create a custom theme for an existing template.
Request you to kindly provide me some instructions as to how to start.