Spaghetti Code

An abstraction of the design from the structure of the website brings decisive advantages. The higher this is, the more independent (separate) they are from each other. No such separation is called a so-called spaghetti code or tag soup (tag from html tag).

Today it's possible to save colours, typography, images of the design and to a large extent even the layout of a website in separate CSS files (CSS = Cascading Style Sheet) without any problems.

This massively reduces the effort for the maintenance of the website. Using CSS, the corporate design can be centrally controlled without the need for developers. This is even possible without restrictions across larger or even several websites.

The central storage of the design in CSS files also reduces the size of the HTML pages massively, which requires faster download times as well as less bandwidth and transfer volume. If pages load faster, the user is pleased and the reduced consumption of resources reduces costs.

Furthermore, this increases the accessibility of the website and makes it more search engine friendly.

While the structure and content of professional websites with management systems are usually read from databases, if they are not already in the server cache, the few required CSS files can be stored on the web server without disadvantages in the file system, which means that queries can be answered very quickly. Once the browser has loaded the CSS files, they do not need to be downloaded again for further page requests. With spaghetti code this decisive advantage is not applicable, as structure, content and design are mixed.
Professional, up-to-date content management systems allow the editing of these CSS files.

The highest possible separation of design also gives designers and developers more independence.
This allows the developer to concentrate on developing a user-friendly, easily accessible website and does not have to bother with the design.
At the same time, the designer can prepare the graphics and the definitions for colours and typography if these do not already exist.

CSS files can be validated like (X)HTML files, which is very useful for error analysis. In any case, we recommend checking CSS files before publishing them.
jigsaw.w3.org/css-validator
Professional content management systems have integrated this checking function to some extent, which is useful in any case.

Tools:
seven49.net - Qualification and Validation Tool (free of charge)