Accessible website experience is a basic requirement, and CSS improves accessibility through style design. 1. Use high-contrast colors (at least 4.5:1), avoid using only colors to transmit information, and should combine icons or text prompts; 2. Ensure that the focus elements are visible, and customize focus styles such as box-shadow, and do not hide at will: focus-visible; 3. Keep the visual consistency with the DOM structure, avoid order attributes disrupting the order, and use ARIA to supplement the instructions if necessary; 4. Control the font size, use relative units (rem/em), and the main text is not less than 16px, allowing users to zoom the page text.

OK, the accessibility website experience is not an additional feature, but a basic requirement. CSS plays an important role in this regard, and while it does not directly deal with logical issues such as semantics or keyboard navigation, accessibility can be significantly improved through reasonable styling and structural arrangement. Here are some practical CSS best practices.

Use high contrast color combination

The contrast between text and background is the key to whether users can see the content clearly. Especially for those with visual impairment and color blind people, low-contrast text is almost impossible to read.

• It is recommended to use a comparison ratio of at least 4.5:1 (large text can be accepted by 3:1).
• Tool recommendation: You can use WebAIM Contrast Checker to test whether the color meets the standard.
• Avoid using color as the only way to pass information. For example, relying on red to represent error messages only, you should combine icons or text prompts.

For example, if a form verification error message is displayed in red only, "Please check input", it will be difficult for color blind users to understand. An icon should be added or explicitly state which one is wrong.

Make sure the focus elements are visible

Keyboard users rely on focus indicators to navigate the page. If you use outline: none; to remove the default outline and there is no alternative, they will be lost in the page.

• If you want to customize the focus style, make sure it is clearly visible. For example, use colored borders or inner shadows:

   a:focus, button:focus {
    outline: none;
    box-shadow: 0 0 0 2px rgba(0, 123, 255, 0.5);
  }

• Don't hide the :focus-visible element unless you have a more suitable alternative.

• The test method is simple: use the keyboard tab key to browse the web page to see if there is any obvious change in each clickable element.

Keep your vision consistent with the DOM structure

Screen readers read page content in HTML structure, and CSS may affect the order of visual rendering. If inconsistent, it will cause the user to hear something and the layout they see.

• Try to avoid using order attribute to disrupt the layout order.
• When using Flexbox or Grid, be careful not to make the visual order too different from the code order.
• If you really need to adjust the order, you can add additional instructions through the ARIA properties.

For example: If you put the main content behind HTML but use CSS to line it up, the screen reader will still read from top to bottom, and the user may first hear the sidebar content and then the main title, causing confusion.

Control font size and scalability

Too small text will make many users unable to see clearly, especially on mobile devices. Reasonable setting of font size and allowing browser scaling is one of the key points to improve accessibility.

• When setting the font size, use relative units (such as rem and em ) instead of pixels.
• The main text is recommended to be no less than 16px (converted to 1rem ).
• Do not set text-size-adjust: none; otherwise the user will be prevented from manually enlarging the page text.

In addition, try to avoid frequent changes in font size in responsive design, which will make users feel confused.

Basically that's it. CSS is done well, not only makes the website look more professional, but also makes it smooth for more people to use it. Some details seem simple but are easily overlooked.

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