What is a theme

A theme is a set of templates, modules, global content and style settings that can be used to create a website. Themes can be downloaded from the Marketplace, while Hub CMS accounts also have access to HubSpot's default themes .

The templates of the pages, be they website or landing page, use a system of sections with the method of "drag & drop area".
The outermost container in a drag-and-drop (dnd) area is called a section. Sections cannot be nested in any other dnd element, but can contain forms, rows, and columns.
Sections can be edited and dragged into the page editor by content creators.
Sections can be styled with their own backgrounds and padding.