A template or theme is a kind of visual editing pattern that is placed on the top of content. A template defines the colors, character fonts, font sizes, background images, spacing, and partitioning of the page, in other words, everything that has to do with the appearance of a page.
A template is made up of at least one HTML file for the structure of the page and one CSS file for the design.
Templates have the big advantage that the design of a website can be completely changed without altering the content.
Content management systems usually have different templates for the frontend and the backend.
A few examples for the use of different templates, which renders the same content: