选择器 | 例子 | 例子描述 | CSS |
---|---|---|---|
.class | .intro | 选择 class="intro" 的所有元素。 | 1 |
#id | #firstname | 选择 id="firstname" 的所有元素。 | 1 |
* | * | 选择所有元素。 | 2 |
element | p | 选择所有 元素。 |
1 |
element,element | div,p | 选择所有 元素和所有
元素。 |
1 |
element element | div p | 选择 元素内部的所有
元素。 |
1 |
element>element | div>p | 选择父元素为 元素的所有
元素。 |
2 |
element+element | div+p | 选择紧接在 元素之后的所有
元素。 |
2 |
[attribute] | [target] | 选择带有 target 属性所有元素。 | 2 |
[attribute=value] | [target=_blank] | 选择 target="_blank" 的所有元素。 | 2 |
[attribute~=value] | [title~=flower] | 选择 title 属性包含单词 "flower" 的所有元素。 | 2 |
[attribute|=value] | [lang|=en] | 选择 lang 属性值以 "en" 开头的所有元素。 | 2 |
:link | a:link | 选择所有未被访问的链接。 | 1 |
:visited | a:visited | 选择所有已被访问的链接。 | 1 |
:active | a:active | 选择活动链接。 | 1 |
:hover | a:hover | 选择鼠标指针位于其上的链接。 | 1 |
:focus | input:focus | 选择获得焦点的 input 元素。 | 2 |
:first-letter | p:first-letter | 选择每个 元素的首字母。 |
1 |
:first-line | p:first-line | 选择每个 元素的首行。 |
1 |
:first-child | p:first-child | 选择属于父元素的第一个子元素的每个 元素。 |
2 |
:before | p:before |
在每个 元素的内容之前插入内容。content属性值: string、url、counter(name)counter(name, list-style-type)counters(name, string) counters(name, string, list-style-type)、attr(X)、open-quote、close-quote、 no-open-quote、no-close-quote |
2 |
:after | p:after | 在每个 元素的内容之后插入内容。 |
2 |
:lang(language) | p:lang(it) | 选择带有以 "it" 开头的 lang 属性值的每个 元素。 |
2 |
element1~element2 | p~ul | 选择前面有 元素的每个
|
3 |
[attribute^=value] | a[src^="https"] | 选择其 src 属性值以 "https" 开头的每个 元素。 | 3 |
[attribute$=value] | a[src$=".pdf"] | 选择其 src 属性以 ".pdf" 结尾的所有 元素。 | 3 |
[attribute*=value] | a[src*="abc"] | 选择其 src 属性中包含 "abc" 子串的每个 元素。 | 3 |
:first-of-type | p:first-of-type | 选择属于其父元素的首个 元素的每个 元素。 |
3 |
:last-of-type | p:last-of-type | 选择属于其父元素的最后 元素的每个 元素。 |
3 |
:only-of-type | p:only-of-type | 选择属于其父元素唯一的 元素的每个 元素。 |
3 |
:only-child | p:only-child | 选择属于其父元素的唯一子元素的每个 元素。 |
3 |
:nth-child(n) | p:nth-child(2) | 选择属于其父元素的第二个子元素的每个 元素。 |
3 |
:nth-last-child(n) | p:nth-last-child(2) | 同上,从最后一个子元素开始计数。 | 3 |
:nth-of-type(n) | p:nth-of-type(2) | 选择属于其父元素第二个 元素的每个 元素。 |
3 |
:nth-last-of-type(n) | p:nth-last-of-type(2) | 同上,但是从最后一个子元素开始计数。 | 3 |
:last-child | p:last-child | 选择属于其父元素最后一个子元素每个 元素。 |
3 |
:root | :root | 选择文档的根元素。 | 3 |
:empty | p:empty | 选择没有子元素的每个 元素(包括文本节点)。 |
3 |
:target | #news:target | 选择当前活动的 #news 元素。 | 3 |
:enabled | input:enabled | 选择每个启用的 元素。 | 3 |
:disabled | input:disabled | 选择每个禁用的 元素 | 3 |
:checked | input:checked | 选择每个被选中的 元素。 | 3 |
:not(selector) | :not(p) | 选择非 元素的每个元素。 |
3 |
::selection | ::selection | 选择被用户选取的元素部分。只能设置两个属性,一个就是background,另一个就是color属性 | 3 |
在css3.info网站上面可以测试当前浏览器对CSS选择器的兼容程度。测试不包括:hover,:active, :focus,:selection,:visited,:link。
IE8 | IE7 | IE6 |
|
|

The roles of HTML, CSS and JavaScript in web development are: 1. HTML is used to build web page structure; 2. CSS is used to beautify the appearance of web pages; 3. JavaScript is used to achieve dynamic interaction. Through tags, styles and scripts, these three together build the core functions of modern web pages.

Setting the lang attributes of a tag is a key step in optimizing web accessibility and SEO. 1) Set the lang attribute in the tag, such as. 2) In multilingual content, set lang attributes for different language parts, such as. 3) Use language codes that comply with ISO639-1 standards, such as "en", "fr", "zh", etc. Correctly setting the lang attribute can improve the accessibility of web pages and search engine rankings.

HTMLattributesareessentialforenhancingwebelements'functionalityandappearance.Theyaddinformationtodefinebehavior,appearance,andinteraction,makingwebsitesinteractive,responsive,andvisuallyappealing.Attributeslikesrc,href,class,type,anddisabledtransform

TocreatealistinHTML,useforunorderedlistsandfororderedlists:1)Forunorderedlists,wrapitemsinanduseforeachitem,renderingasabulletedlist.2)Fororderedlists,useandfornumberedlists,customizablewiththetypeattributefordifferentnumberingstyles.

HTML is used to build websites with clear structure. 1) Use tags such as, and define the website structure. 2) Examples show the structure of blogs and e-commerce websites. 3) Avoid common mistakes such as incorrect label nesting. 4) Optimize performance by reducing HTTP requests and using semantic tags.

ToinsertanimageintoanHTMLpage,usethetagwithsrcandaltattributes.1)UsealttextforaccessibilityandSEO.2)Implementsrcsetforresponsiveimages.3)Applylazyloadingwithloading="lazy"tooptimizeperformance.4)OptimizeimagesusingtoolslikeImageOptimtoreduc

The core purpose of HTML is to enable the browser to understand and display web content. 1. HTML defines the web page structure and content through tags, such as, to, etc. 2. HTML5 enhances multimedia support and introduces and tags. 3.HTML provides form elements to support user interaction. 4. Optimizing HTML code can improve web page performance, such as reducing HTTP requests and compressing HTML.

HTMLtagsareessentialforwebdevelopmentastheystructureandenhancewebpages.1)Theydefinelayout,semantics,andinteractivity.2)SemantictagsimproveaccessibilityandSEO.3)Properuseoftagscanoptimizeperformanceandensurecross-browsercompatibility.


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