Mastering CSS: Understanding the Cascade

Cascading Style Sheets (CSS) is a fundamental technology of the web, allowing developers to control the visual presentation of HTML documents. While CSS syntax may seem simple at first glance, the way styles are applied and inherited can be surprisingly complex. Understanding these intricacies is crucial for writing efficient, maintainable, and predictable CSS.
In this comprehensive guide, we'll explore the cascade and inheritance concepts of CSS.

The CSS Cascade

The cascade is the algorithm that determines which CSS rules are applied to elements when multiple conflicting rules exist. It's essential to understand how the cascade works to write CSS that behaves as expected. The cascade considers several factors in the following order:

• 1 Stylesheet origin
• 2 Inline styles
• 3 Selector specificity
• 4 Source order

To be completely exhaustive, we can add:

• 2.5 Styles that are defined in layers read more
• 3.5 Styles that are scoped to a portion of the DOM read more

Let's break down the factors that influence the cascade, in order of precedence:

1. Stylesheet Origin

CSS can come from three different sources:

• 1 User-agent styles: These are the browser's default styles. Each browser has its own set of default styles, which is why unstyled HTML can look slightly different across browsers.
• 2 User styles: These are custom styles set by the user. While rare, some users may have custom stylesheets to override default styles for accessibility or personal preference.
• 3 Author styles: These are the styles you write as a web developer.

Generally, author styles take precedence over user styles, which in turn override user-agent styles. This allows developers to customise the appearance of elements while still respecting user preferences when necessary.

2. Inline Styles

Styles applied directly to an element using the style attribute have very high priority:

<p style="color: red;">This text will be red.</p>

Inline styles will override any styles defined in external stylesheets or