Why inline styles have lower priority than CSS

In web development, we often use

The Concept of Specificity

In CSS, specificity determines the importance of which style rules apply to an element. When an element is affected by multiple style rules, the browser determines which style to apply based on the specificity of those rules. The priority rules of CSS are as follows:

Inline styles have the highest priority and override both external and inline styles.
Inline styles have the next highest priority and override external styles.
External styles have the lowest priority.

This means that if an element is affected by both an inline style and an external style, the inline style will override the external style. But why do inline styles have lower priority than CSS? We’ll explain this from several perspectives.

Maintainability

Inline styles are typically written directly within the style attribute of an HTML tag. This approach conflates the structure and style of a web page, making it difficult to maintain and manage code. When modifying a style, developers have to find every place where the inline style is used and make the changes, which is obviously inefficient and inefficient.

In contrast, centralizing styles in CSS files allows for better separation of structure and style, improving code maintainability. The cascading nature of CSS helps developers more easily manage and modify styles without intermingling them within HTML tags.

Readability

Inline styles complicate and lengthen the attribute values of HTML tags, reducing code readability. When styles are written directly within tags, it’s difficult to visually identify the style of an element, making it difficult for other developers to quickly understand the code.

CSS style rules are organized based on selectors and attribute values, clearly expressing element styles. Introducing styles through methods like class selectors and ID selectors makes code more concise and easier to read and understand.

Maintainability

The lower priority of inline styles is due to concerns about code maintainability. Centralizing styles in CSS files makes code more modular and maintainable. By introducing external style sheets, you can easily reuse styles, reduce code redundancy, and improve development efficiency.

Performance

When a browser parses an HTML document, it applies style rules to the corresponding elements. If you use a lot of inline styles, the browser will have to parse the style attribute for each element, which will increase page load time and reduce performance.

In contrast, centralizing styles in an external style sheet allows the browser to download the style sheet file only once and cache it, reducing the number of reloads. This speeds up page loads, reduces server requests, and improves performance.

Real-World Example

Let’s use an example to demonstrate why inline styles have lower specificity than CSS.

<!DOCTYPE html> 
<html lang="en"> 
<head> 
<meta charset="UTF-8"> 
<meta http-equiv="X-UA-Compatible" content="IE=edge"> 
<meta name="viewport" content="width=device-width, initial-scale=1.0"> 
<title>Inline Style vs CSS</title> 
<style> 
p { 
color: red; 
} 
</style> 
</head> 
<body> 
<p style="color: blue;">This is a paragraph with inline style</p> 
</body> 
</html>

In the example above, we added inline style style="color: blue;">This is a paragraph with inline style</p> </body> </html>

In the example above, we added inline style style="color: blue;">This is a paragraph with inline style</p> </body> </html> blue;” sets the text color to blue. However, because the style rule in CSS has a higher precedence than the inline style, the final paragraph text color remains red.

This example demonstrates the precedence rules of CSS. Even though the inline style explicitly sets the color to blue, the external style sheet sets the color to red, so the final effect is still based on CSS.

Conclusion

To summarize, there are three main reasons why inline styles have lower precedence than CSS: maintainability, readability, and performance. Inline styles mix structure and style, reducing code maintainability; inline styles make code more complex and lengthy, reducing readability; and inline styles increase page load time and reduce performance.

Therefore, in actual web development, we should avoid using inline styles directly whenever possible and instead centralize styles in external style sheets to improve code maintainability, readability, and performance. This allows for better utilization of CSS precedence rules, making the application of style rules more flexible and efficient.