Why doesn't css background appear?

HTML5, CSS and JavaScript should be efficiently combined with semantic tags, reasonable loading order and decoupling design. 1. Use HTML5 semantic tags, such as improving structural clarity and maintainability, which is conducive to SEO and barrier-free access; 2. CSS should be placed in, use external files and split by module to avoid inline styles and delayed loading problems; 3. JavaScript is recommended to be introduced in front, and use defer or async to load asynchronously to avoid blocking rendering; 4. Reduce strong dependence between the three, drive behavior through data-* attributes and class name control status, and improve collaboration efficiency through unified naming specifications. These methods can effectively optimize page performance and collaborate with teams.

To create responsive images using CSS, it can be mainly achieved through the following methods: 1. Use max-width:100% and height:auto to allow the image to adapt to the container width while maintaining the proportion; 2. Use HTML's srcset and sizes attributes to intelligently load the image sources adapted to different screens; 3. Use object-fit and object-position to control image cropping and focus display. Together, these methods ensure that the images are presented clearly and beautifully on different devices.

InCSS,propertyinheritanceaffectshowstylesarepassedfromparentelementstochildren.Somepropertieslikecolorandfont-familyinheritbydefault,applyingtoallnestedelementsunlessoverridden.Non-inheritedpropertiessuchasborder,margin,andpaddingmustbesetexplicitly.

The:has()pseudo-classinCSSallowstargetingaparentelementbasedonitschildelements.Itworksbyusingthesyntaxparent:has(child-selector)toapplystylesconditionally.Forexample,div:has(img)appliesstylestoadivcontaininganimage.Multipleselectorscanbeusedwithcomma

opacity is an attribute in CSS that controls the overall transparency of an element, with values ranging from 0 (fully transparent) to 1 (fully opaque). 1. It is often used for the image hover fade effect, and enhances the interactive experience by setting the opacity transition; 2. Making a background mask layer to improve text readability; 3. Visual feedback of control buttons or icons in the disabled state. Note that it affects all child elements, unlike rgba, which only affects the specified color part. Smooth animation can be achieved with transition, but frequent use may affect performance. It is recommended to use it in combination with will-change or transform. Rational application of opacity can enhance page hierarchy and interactivity, but it should avoid interfering with users.

Use the ::selection pseudo-element of CSS to customize the highlighting style when the web page text is selected to improve the aesthetics and unity of the page. 1. Basic settings: define background-color and color through ::selection, such as yellow background with dark gray fonts; specific elements such as p::selection can also be limited. 2. Compatibility processing: Add the -webkit- prefix to be compatible with Safari and mobile browsers, and the Firefox and Edge standards are well supported. 3. Pay attention to readability: Avoid excessive color contrast or too fancy, and should be coordinated with the overall design. For example, choose a soft blue base in dark mode to improve visual comfort. Reasonable use can enhance the texture of the interface, ignore details

Word-break and overflow-wrap (formerly word-wrap) do differently when dealing with long words or unbreakable content. 1. Word-break controls how to break lines of words in block elements, break-all forces long words to break, keep-all avoids breaking, suitable for Chinese, Japanese and Korean texts. 2. Overflow-wrap disconnects long words when necessary to prevent overflow, break-word makes the context more intelligent. 3. In usage scenarios, use word-break:break-all for code, and use overflow-wrap:break-word for user comments. 4. Pay attention to differences in browser compatibility and different mobile behaviors

list-style is abbreviation attribute in CSS for controlling the pre-marking style of list items. 1. You can set the list-style-type, list-style-position and list-style-image at the same time; 2. By default, unordered lists use disc styles, and ordered lists use numeric numbers; 3. Support setting types, positions and pictures, and specify backup styles to deal with image loading failures; 4. In actual development, the default styles are often cleared to ensure consistency, and pay attention to text indentation and image loading issues.