The key to mastering modern CSS design is layout, responsiveness, and maintainability. 1. Use CSS Grid and Flexbox to combine layout. Grid is suitable for two-dimensional structures such as the entire page, and Flexbox is suitable for one-dimensional arrangements such as button groups; 2. Use CSS variables to achieve theme switching, define color variables and dynamic switching with JavaScript; 3. Mobile priority and handle responsive details, adopt relative units, picture srcset attributes and centralized media queries; 4. Improve maintainability, use BEM and other naming specifications, split modules, control nesting levels, and separate components and layout styles. These combinations of techniques can significantly improve code quality.

When writing CSS in modern web design, the key is not to master how many selectors or animation attributes, but to understand layout, responsiveness and maintainability. Many people get stuck after learning basic CSS and don’t know how to write more flexible and modern style code. This article talks about several advanced but practical techniques to help you break through this bottleneck.

Combined layout with CSS Grid and Flexbox

Flexbox is good at one-dimensional layouts (such as navigation bars, button groups), while Grid is more suitable for two-dimensional layouts (such as the entire page structure). The two are not substitute relationships, but complementary.

To give a practical example: you make a dashboard page, with the sidebar on the left and the content area on the right. Grid can be used to divide the overall structure:

 .dashboard {
  display: grid;
  grid-template-columns: 250px 1fr;
}

Then use the Flexbox layout card components in the content area:

 .cards {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
}

This combination not only keeps the overall structure clear, but also makes the internal elements more flexible.

suggestion:

• First use Grid to divide large areas
• Then use Flexbox to process element arrangement in the area
• Don't force yourself to solve the problem with just one solution

Flexible use of CSS variables to achieve topic switching

CSS custom properties (that is, variables often referred to as variables) are not just to write less duplicate values, its real benefit is to dynamically control the style.

For example, you can define a set of color variables:

 :root {
  --primary-color: #4a90e2;
  --bg-color: #f5f5f5;
}

Then refer to these variables in the component:

 .button {
  background-color: var(--primary-color);
}

Want to change the theme? Just change the variable value:

 .dark-theme {
  --primary-color: #6ec1ff;
  --bg-color: #1a1a1a;
}

Coupled with JavaScript to dynamically switch class names, you can realize one-click switching between night mode/day mode.

Tips:

• Focus variables in :root or topic class management
• Automatically recognize dark mode with media query
• Can be compatible with old browsers using PostCSS plug-in

Detailed handling of mobile-first responsive design

"Mobile First" is no longer a new concept, but many people just add the meta viewport tag and just finish it. A truly responsive design should consider breakpoint settings, font adaptation, picture scaling and other aspects.

Recommended practices are:

• Start writing styles from a small screen and gradually enhance them
• Use relative units (em/rem/vw/vh)
• Images are matched with srcset and sizes attributes with max-width: 100%
• Media queries should be concentrated inside components, not individual files

For example, a responsive image component can be written like this:

 <img src="/static/imghw/default1.png"  data-src="small.jpg"  class="lazy" 
  srcset="small.jpg 480w, medium.jpg 800w, large.jpg 1200w"
  sizes="(max-width: 600px) 100vw, 800px"
  alt="Example Picture"
/>

In this way, the browser will automatically select the most suitable image to load according to the device width, saving traffic and improving performance.

Write out a CSS structure that is easier to maintain

As the project gets bigger, CSS can easily become messy. In order to avoid the problem of "not daring to delete" in the later stage, it is recommended to pay attention to the organization method from the beginning.

Common practices are:

• Use naming specifications like BEM or SMACSS
• Split CSS into modules (such as _buttons.scss , _layout.scss )
• Avoid excessive nesting, and control the level within 3 layers
• Component style and layout style are written separately

If you are using a tool-first framework like Tailwind or Bootstrap, be careful not to rely on utility class to build it. Appropriately abstracting some reused classes can make the code clearer.

Basically that's it. Advanced CSS does not mean that you need to use a cool feature, but knows when and what methods to use to write style codes with clear structure, strong scalability and convenient maintenance. Many techniques seem simple, but when combined, they are the key to modern web design.

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