Understanding Cascading Style Sheets (CSS)

Cascading Style Sheets, often referred to as CSS, is a style sheet language that describes the look and formatting of a document written in HTML or XML and its related dialects. This includes visual aspects such as layout, colors, and fonts. It allows developers and designers to manipulate these elements across all pages of a website, thus maintaining consistency and making it easier if updates are required.

Web browsers apply CSS rules to select elements and apply styles. The 'cascading' aspect of CSS comes from the rules of priority the browser follows to determine which styles apply if more than one rule matches a particular element. This cascading hierarchy or priority scheme simplifies defining complex style scenarios.

Principally, CSS helps to separate the content of a webpage (handled mostly by HTML) from its presentation layer (handled by CSS). This separation enhances content accessibility and provides more flexibility and control over presentation elements.

CSS has a wide range of applications. Let's consider a practical example. Suppose you have a website with hundreds of pages. You want all the headings on your site to be blue. If you were using just HTML, you'd have to go to each page and edit the code for every single heading. But with CSS, you just change one line of code, and all your headings update automatically.

In terms of best practices when using CSS, here are few to consider:

• Use readable and brief CSS selectors.
• Use shorthand properties to reduce the size of your code.
• Comment your code for better understanding and readability.
• Consider using a CSS preprocessor like SASS or LESS to enhance functionality.
• Always organize your CSS code into a logical structure. It makes the code easier to understand, maintain, and debug.

In summary, CSS or Cascading Style Sheets is a powerful tool for web designers and developers. It is an essential part of modern web design and is crucial for creating a consistent, efficient, and accessible webpage. It not only brings a heap of practical benefits but also is in line with the principles of good web design.