Improving Style Recalculation Speed with CSS
Published: 2024-03-21 01:41:35

In the fast-paced global landscape of modern web development, the performance of a website is frequently the first and last impression it leaves on its users. As web developers and designers attempt to create visually appealing and feature-rich websites, ensuring optimal speed becomes increasingly important. Improving the speed of style recalculation with CSS is an important part of this performance optimization.

In this article, we'll explore how to improve style recalculation in CSS as well as the significance of this process in modern web development. We will also investigate the effect of style recalculation on web page speed, analyze important CSS performance bottlenecks, and give practical insights and methods for improving the performance of your web projects. 

## Understanding Style Recalculation
Style recalculation is the process by which a browser calculates the final style of an element. This procedure is initiated anytime the DOM (Document Object Model) is altered, such as when an element is added, removed, or modified. During this process, the browser determines the styles that should be applied to each element. It is the browser's means of ensuring that web pages are displayed to users as intended. It is crucial to establish how elements are styled, positioned, and scaled on a web page. This process ensures that text is legible, graphics are properly aligned, and the overall design is authentically copied.

Let's get started with some real code samples to help you grasp style recalculation.
```html
<!DOCTYPE html>
<html>
<head>
    <style>
        .container {
            width: 80%;
            height: 80vh
            margin: 0 auto;
            padding: 20px;
            background-color: #f0f0f0;
        }
        .box {
            width: 50%;
            float: left;
            padding: 10px;
            background-color: #3498db;
            color: #fff;
            text-align: center;
        }
    </style>
</head>
<body>
    <div class="container">
        <div class="box">Box 1</div>
        <div class="box">Box 2</div>
        <div class="box">Box 3</div>
    </div>
</body>
</html>
```
From the code above, we created a simple layout with three boxes inside a containercontainer. CSS styles define the `width`, `margin`, `padding`, and `background colors` of these components. The browser calculates the `container` and `box` styles, taking into account the `width`, `margin`, `padding`, and `background colors`. In addition, the browser resolves mismatched styles, ensuring that each element is properly styled, like the image below:

![box.PNG](https://hackmd.io/_uploads/HJkjgmHQT.png)

## Common CSS Performance Bottlenecks
CSS is the foundation of online design, allowing developers to construct visually appealing and responsive websites. Inefficient or poorly designed CSS, on the other hand, can cause performance bottlenecks, resulting in slow page loading times and a poor user experience. To sustain a fast and efficient website, it's important to understand typical CSS performance bottlenecks and how to avoid them. Let's look at key CSS performance bottlenecks and their wrong and correct solutions in the example code:

* Overuse of !important: The !important flag should be used with caution, as it can cause specificity battles and make maintaining your CSS difficult. When everything is designated as !important, managing and debugging styles becomes difficult.
```css
/* Avoid overusing !important: */
.title {
    color: #FF0000 !important;
}

/* Prefer specificity: */
.title {
    color: #FF0000;
}
```
* Excessive Use of Complex Selectors: Complex selectors require the browser to scan the whole DOM tree, making matching items with the provided rules slower.  For example, selecting items with deeply nested structures or applying styles based on attributes like data might be time-consuming.
```css
/* Inefficient: */
ul > li > a {
    color: #FF0000;
}

/* Efficient: */
.nav-link {
    color: #FF0000;
}
```
* High Specificity: When many conflicting rules exist, CSS specificity determines which styles are applied to an element. High specificity rules take precedence over lesser specificity rules; however, they can increase calculation time when computing styles.
```css
/* High Specificity: */
#main .content .article .title {
    font-weight: bold;
}

/* Lower Specificity: */
.title {
    font-weight: bold;
}
```

## CSS Best Practices for Performance
Regardless of the type of your website or if it operates well in several web browsers, it must load promptly. Your users will leave if it is not fast enough. CSS, on the other hand, can constitute a substantial barrier to web page performance if not improved. It is critical to follow CSS best practices for performance to guarantee that your web pages load quickly and deliver a consistent user experience. we'll consider These essential points to keep in mind:

*  Minimize HTTP Requests: To accomplish this, we must combine and minify many CSS files into a single file to reduce the number of requests performed by the browser.

* Use External Stylesheets: Rather than embedding CSS in HTML files, use external stylesheets. This allows the browser to cache the CSS file, which speeds up subsequent page views.

* Prioritize Critical CSS: Loads critical CSS inline within the HTML section to guarantee that above-the-fold material is styled as soon as possible. Non-critical CSS should be loaded asynchronously or after the page has loaded.

* Optimize CSS Selectors: Use efficient and specific CSS selectors. To improve efficiency, reduce selector complexity, and minimize the use of universal selectors.

* Minify CSS: To reduce the size of your CSS files, remove extraneous characters and whitespace. Many tools and build processes can minify your CSS automatically.

* Use Media Queries Wisely: For responsive design, use well-thought-out media queries. Excessively massive or unoptimized media queries might cause page rendering to lag.

## Profiling and Benchmarking CSS Performance
Benchmarking CSS performance entails running controlled experiments to determine the rendering speed of web pages under various scenarios. This method can assist in determining how different CSS methods affect website load speeds.

### Using the Layout or Reflow Panel
In web development, the Layout or Reflow panel in browser developer tools is a significant resource for spotting style recalculation errors and understanding how changes in your CSS affect the rendering of web pages. This window allows you to view the layout process in action and identify areas where you may improve your CSS. Here's how to utilize it:

1. open the developer tools in your browser.  Developer tools are typically accessed by hitting F12 or right-clicking on a web page element and selecting Inspect.
2. Navigate to the Layout or Reflow panel. The exact location of this panel may differ based on the browser you are using. In Google Chrome, it is found under the **Performance** tab.
```html
<!DOCTYPE html>
<html>
<head>
    <style>
        /* Sample CSS for demonstration */
        .box {
            width: 100px;
            height: 100px;
            background-color: #3498db;
        }
    </style>
</head>
<body>
    <div class="box"></div>
    <button onclick="changeColor()">Change Color</button>

    <script>
        // JavaScript function to change the box color
        function changeColor() {
            const box = document.querySelector('.box');
            box.style.backgroundColor = '#e74c3c';
        }
    </script>
</body>
</html>
```
The code above shows a simple `HTML` document with a `box` and a `button`. The `background color` of the `box` changes when you click the `button`, like this:

![rec21](https://hackmd.io/_uploads/HJP86PJNp.gif)

We'll use the Layout or Reflow panels to check how this change affects the rendering.

3. Click the **Record** button to begin a profiling session in the Layout or Reflow panel. You can interact with the web page to cause layout changes. In the example, clicking the button changes the box's background color. 
4. Stop the recording in the Layout or Reflow panel after you've made changes to the page. A thorough report of the layout activity will be displayed. Look for entries indicating style recalculations or layout changes, like the clip below from Google Chrome:

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/vqx2m779u6xviysx7n3i.gif)

From the example above, you can see the report of the layout and reflow activities and how changing the color of the box changes the layout and causes a reflow. For more details, visit [Chrome for Developers Documentation.](https://developer.chrome.com/docs/devtools/performance/?utm_source=devtools)

## CSS Specificity and Efficiency
CSS specificity refers to how browsers assess the importance, relevance, and seniority of CSS styles. It determines which styles take precedence when there are conflicting regulations. CSS specificity is determined by the combination of selectors used to target an element. The more specific a selector is, the higher its specificity.

Specificity is often calculated using the following factors, sorted from highest to lowest specificity which are listed below:

* Inline Styles
```html
<p style="color: red;">Hello world</p>
``` 
* ID Selectors
```css
#container {
    color: blue;
}
```
* Class and Attribute Selectors
```css
.highlight {
    background-color: yellow;
}

[data-theme="dark"] {
    color: white;
}
```
* Type Selectors
```css
p {
    font-weight 5px;
}
```
* Universal Selectors
```css
* {
    margin: 0;
}
```
understanding CSS Specificity and Efficiency helps you to design a more maintainable CSS code and avoid typical issues associated with specificity and the abuse of high-specificity rules.

## CSS Preprocessors and Performance
What do you think about CSS? Do you believe that all CSS strategies are the same? If so, it's time to reconsider your attitude toward this vital programming language. While implementing CSS code directly within your stylesheets is common when developing a small application, larger projects are a different matter.

CSS preprocessors like Sass, Less, and Stylus have gained popularity among web developers due to their ability to simplify and improve the process of writing and maintaining CSS. CSS preprocessors, on the other hand, are programming languages that enhance the capabilities of regular CSS. They enable developers to employ variables, functions, nested rules, and other capabilities, making complicated stylesheets easy to manage and maintain.

Although CSS preprocessors have many advantages, they might have an impact on web performance if not utilized correctly. Here are some important factors to consider:

* Increased File Size: When compared to manually generated stylesheets, preprocessors frequently generate bigger CSS files. This can result in longer download times, which affects page load speed, particularly on slower network connections.
* CSS Preprocessor Compilation Overhead: CSS preprocessors must be compiled into regular CSS before they can be sent to browsers.
* Complex Selectors: Preprocessor nesting can result in the development of complex and very specific selectors. These selectors have the potential to degrade rendering and selector matching performance.
* Unused Code: If variables, mixins, or functions are not carefully maintained, preprocessors can generate unused or redundant code. This can result in bigger CSS files and poorer performance.

## Responsive Design and CSS Performance
Responsive design is a web design method that seeks to make online sites look and perform properly across a variety of devices, such as desktop computers, laptop computers, tablets, and mobile phones.

From 2013 to today, the number of people turning to Responsive Web Design as a way to give a consistent experience across multiple screen resolutions has increased significantly.

why?

Web visitors want a consistent experience regardless of device. As a result, if a user views your site and it is not optimized for their machine, she is likely to leave and never return.

![](https://hackmd.io/_uploads/HkrjNJJXT.jpg)

To ensure responsive design doesn't compromise web performance, we'll recommend the following:

* Aim for clean, brief CSS. Remove any unnecessary rules, and concentrate on maintaining specificity.
* Reduce file sizes, and minify and compress your CSS files before publishing.
* Use responsive image approaches like srcset and picture elements to provide images that are suitably sized depending on your device's capabilities. 
* To ensure optimal website load speeds, set and stick to performance goals that include CSS size and rendering times.
* Lastly, Frequently monitor your site's performance on different devices and screen sizes, making adjustments as needed.
 
## CSS-in-JS and Runtime CSS Generation
The idea of generating CSS with JavaScript has grown in popularity in recent years, owing partly to the dominance of reactive frameworks such as React and Svelte. These frameworks do not need the use of JavaScript to style components, but they do allow for it. As a result, a variety of CSS-in-JS frameworks have emerged to facilitate the process.

Inline definition and loading from an external file are the only options for old-school CSS. The browser loads the CSS, parses it, and then applies the styles to the markup in both circumstances. CSS-in-JS provides a third option for distributing CSS by producing it programmatically in code.

CSS-in-JS provides a syntax for converting JavaScript into browser-applicable styles. 

Listing CSS-in-JS with styled-components:
```javascript
import styled from 'styled-components';

// Define a styled component
const Button = styled.button`
  background-color: #3498db;
  color: #fff;
  padding: 10px 20px;
  border: none;
  border-radius: 4px;
  cursor: pointer;

  &:hover {
    background-color: #2980b9;
  }
`;

// Render the styled component
function App() {
  return (
    <div>
      <Button>Click me</Button>
    </div>
  );
}
```
From the code above, styles are contained within the component, which improves maintainability and lowers the danger of style conflicts. CSS-in-JS is an attempt to make difficult use cases easier to manage, therefore don't use it in places where it isn't needed. Also, ensure to install styled components like so:
```
npm install styled-components
```
### Runtime generation with CSS
Runtime CSS generation is a technique that generates a CSS string in JavaScript and then injects it into the document using a style tag. This method generates a Style Sheet, not inline styles.

CSS run-time generation is typically appropriate for apps that lack content that can be used immediately. Typically, such programs, such as Twitter, Facebook, and LinkedIn, require user engagement before they can truly be beneficial to a user. Furthermore, when a user is logged in, no HTML for SEO is required.

Runtime CSS Generation with styled-components:
```javascript
import styled from 'styled-components';
const Button = styled.button`
  background-color: ${props => props.primary ? "#3498db" : "#e74c3c"};
  color: #fff;
  padding: 10px 20px;
  border: none;
  border-radius: 4px;
  cursor: pointer;

  &:hover {
    background-color: ${props => props.primary ? "#2980b9" : "#c0392b"};
  }
`;

// Render the styled component with dynamic theming
function App() {
  return (
    <div>
      <Button primary>Primary Button</Button>
      <Button>Secondary Button</Button>
    </div>
  );
}
```
From the code above, the styles are generated at runtime based on the `primary prop`, allowing for dynamic style changes with no further style recalculation. The perceived performance of such apps can be improved by using placeholders and other methods to make the application appear faster than it is. Such applications are typically data-intensive, thus they will not be as beneficial as an article. 

## Server-Side Rendering (SSR) and Critical CSS
Server-Side Rendering (SSR) and Critical CSS are two critical strategies for improving the performance of style recalculation in online applications. Let's look at how these strategies operate and why they're so important for improving web performance.

### Server-Side Rendering (SSR)
Server Side Rendering (SSR) generates the HTML components of the webpage on the server. When a browser requests an SSR web page, the browser receives a fully completed HTML web page with the HTML components already built.

When you use SSR for server-side style calculation, the server pre-renders the HTML content and applies CSS styles. This means that the critical styles are already applied to the initial HTML response, reducing the requirement for style recalculation on the client side. Like the code below:
```javascript
// Express.js server
import express from 'express';
import React from 'react';
import { renderToString } from 'react-dom/server';
import App from './App';

const app = express();

app.get('/', (req, res) => {
  const appHtml = renderToString(<App />);
  res.send(renderFullPage(appHtml));
});

app.listen(3000, () => {
  console.log('Server is listening on port 3000');
});
```
From the code above, we used SSR with React to render the initial `HTML` on the server, and the key styles are included in the initial `HTML` response, reducing the need for lengthy style recalculation on the client side.

### Critical CSS
Critical CSS is the minimum amount of css required to style a page in its initial state. It's rendered with a style tag in the document's head.  Also, it is an approach that identifies and inlines only the CSS styles required for **above-the-fold** content. By inlining only the styles required for content that is immediately visible in the viewport (above-the-fold), you reduce the initial style computation workload, resulting in a faster-perceived loading speed for your web page. 
```css
/* Critical CSS for above-the-fold content */
.header {
  background-color: #3498db;
  color: #fff;
}

/* Non-critical CSS for below-the-fold content */
.button {
  background-color: #e74c3c;
  color: #fff;
}
```
From the code above, we targeted the critical styles for the `header`, which is considered above-the-fold information. These styles can be inlined in the HTML to reduce style recalculation for the most critical areas of the page.

## Browser Compatibility and Updates 
Today, there are numerous browsers, operating systems, and device alternatives, both modern and legacy, including Windows, Linux, Mac, Internet Explorer, Firefox, Chrome, Safari, and Opera. Each browser or system translates and interprets your website code in order to visually display it, and each does it in its way.

### What is Browser Compatibility
Browser compatibility refers to whether or not a website or web application works as expected in any given browser version on various devices. A website may work smoothly in one browser but have difficulties and errors in others. A good website is cross-browser compatible, meaning it works on all or the majority of browsers (including mobile/tablet versions), with a consistent layout and functionality. The importance of browser compatibility stems from the broad landscape of web browsers and their rendering engines, each of which may read HTML, CSS, and JavaScript slightly differently.

### Browser Compatibility Matrix
During the creation and testing phases of a website, the teams in charge of development and testing frequently have a list of devices and browsers that they expect their sites to perform smoothly with. After it has been established and documented, this list of compatible browsers and devices is been referred to as the browser compatibility matrix or browser support matrix.

Here's a sample of a browser compatibility matrix.

![brower.PNG](https://hackmd.io/_uploads/S1cNtCyX6.png)

Browser compatibility matrix helps developers make informed judgments about which web technologies and features to include in their projects. This contributes to ensuring that websites and online apps give a uniform user experience across browsers. It also aids in determining whether technologies may necessitate fallbacks or alternate solutions for older or non-compliant browsers.

### Browser Updates
Browser updates are releases made regularly by browser vendors (for example, Google, Mozilla, and Microsoft) to improve browser performance, security, and compatibility. Check to see if your [browser is up to date](https://browser-update.org/update-browser.html).

### Why Updates Browser
Updating your web browser is a must for a variety of reasons, which are as follows:

* Security: Browser updates often include essential security patches that safeguard users from vulnerabilities and attacks. 
* Web Standards Compliance: Browser upgrades strive to improve web standards compliance by eliminating rendering disparities between browsers. This helps to improve compatibility.
* Feature Support: New web technologies, APIs, and features are routinely added to modern browsers. Staying current ensures access to the most recent web development features.
* User Experience: To have the greatest web experience possible, users are urged to utilize the most recent browsers. Outdated browsers may be incapable of supporting advanced web functions, resulting in a poor user experience.
* Performance: New browser versions often contain performance improvements, such as streamlining JavaScript execution, rendering speed, and memory utilization. This leads to faster and smoother web experiences.

## Wrapping up
Improving style recalculation speed with CSS is a vital part of web development that has a direct impact on the user experience and overall performance of web applications.
By addressing style recalculation speed and embracing the ideas and strategies mentioned in this article, you can design web applications that not only look amazing but also operate extraordinarily well, regardless of the devices and browsers used by your audiences. This user-centric approach to web development is the foundation of a successful and competitive online presence.