When Is Css Applied

CSS Programming

As a web developer, I often find myself navigating the intricacies of CSS to ensure that the styling of my web pages is just right. One fundamental aspect of CSS that I constantly grapple with is understanding when exactly CSS is applied to HTML elements. Let’s dive deep into this topic to gain a comprehensive understanding.

At Which Point is CSS Applied?

CSS is applied to HTML elements during the rendering phase of a web page. This means that after the browser fetches the HTML and constructs the DOM (Document Object Model) and CSSOM (CSS Object Model), it proceeds to calculate the styles and layout of the page. It’s at this stage that CSS rules are applied to the corresponding HTML elements, resulting in the final visual presentation of the web page.

It’s important to note that CSS can be applied in various ways, such as through external style sheets, internal style sheets, inline styles, or via JavaScript manipulation. Each method has its own specific timing and impact on the rendering process.

External Style Sheets

When an external style sheet is linked to an HTML document using the <link> tag, the CSS rules are fetched along with the HTML content. The browser then applies these styles to the respective HTML elements during the rendering phase.

Internal Style Sheets

Internal style sheets, defined within the <style> tag within the HTML document, are also applied during the rendering phase. The browser reads and applies these styles as it constructs the CSSOM.

Inline Styles

Inline styles, declared directly within the HTML tags using the style attribute, are applied as the browser parses the HTML content. This means that these styles are applied very early in the rendering process, potentially impacting the layout and performance of the page.

JavaScript Manipulation

When CSS is manipulated via JavaScript, such as by adding or modifying styles dynamically, the timing of application depends on when the JavaScript code is executed. This dynamic nature introduces complexities in understanding when exactly the CSS takes effect, especially in relation to the rendering timeline.


Understanding when CSS is applied to HTML elements is crucial for crafting performant and visually appealing web pages. By grasping the timing and intricacies of CSS application, we as web developers can optimize the styling process and enhance the overall user experience of our websites.