Maybe the selectors you always use are :#id  .class  And the label selector . But that's not enough , In order to be more handy in development , This article summarizes 30 individual CSS3 Selectors , I hope that's helpful .

1 *: Universal selector

* { margin:0; padding:0; }

* A selector is to select all the elements on the page , The purpose of the above code is to convert all the elements into margin and padding Set to 0, The most basic way to clear the browser default style .

* Selectors can also be applied to sub selectors , For example, the following code :

#container * { border:1px solid black; }

such ID by container All child tag elements of are selected , And set up border.

2 #id:id Selectors

#container {
width: 960px;
margin: auto;
}

id The selector is very strict and you can't reuse it . We have to be very careful when using it . You need to ask yourself : Do I have to assign a value to this element id To locate it ?

3 .class: Class selectors

.error {
color: red;
}

This is a class Selectors . It goes with id The difference is , It can locate multiple elements . When you want to style multiple elements, you can use class. When you want to modify a particular element, that is to use id To locate it .

4 selector1 selector2: Descendant selector

li a {
text-decoration: none;
}

The next generation selector is More commonly used Selectors . If you want to be more specific about positioning elements , You can use it . for example , If , You don't need to position all of them a Elements , And just positioning li Label under a label ? And then you need to use Progeny The selector is .

Tips : If your selector looks like X Y Z A B.error such , Then you're wrong . Remind yourself all the time , Is it really necessary to modify so many elements .

5 tagName: tag chooser

a { color: red; }
ul { margin-left: 0; }

If you want to locate all the tags on the page , Not through id Or is it ’class’, It's simple , Use the type selector directly .

6 selector:link  selector:visited  selector:hover  selector:active  Pseudo class selector

In general selector All for a label , The meanings of the above four pseudo class selectors are as follows :

link: Connect to the normal state .
visited: After the connection has been accessed .
hover: When the mouse is on the connection .
active: When the connection is pressed .

Not moved into a Tag Links :link
move a Tag Links :link、hover
Click on a Tag Links :link、hover、active

Click and don't move in a When tags are connected :link、visited

Click and move in a When tags are connected :link、visited、hover

Click and then click again a When tags are connected :link、visited、hover、active

This is the style of all combinations .

If there are more than one of the same styles , The latter style will override the former style , So the definition of these four pseudo classes has the requirement of order , And what you're saying is ‘lvha’ That's why .
 
7 selector1 + selector2 : Adjacent selector

ul + p {
color: red;
}
It directs the selection of the immediate successor to the specified element . The above example selects all ul The first paragraph after the label , And set their colors to red .
 
8 selector1 > selector2 : Child selectors

div#container > ul {
border: 1px solid black;
}

The difference is that the latter commander chooses its direct sub element . See the following example :

<div id="container">
<ul>
<li> List Item
<ul>
<li> Child </li>
</ul>
</li>
<li> List Item </li>
<li> List Item </li>
<li> List Item </li>
</ul>
</div>

#container > ul I'll just pick id by ’container’ Of div Under all direct ul Elements . It won't be positioned as the first li Under the ul Elements .
For some reason , There are many performance advantages to using a child node combination selector . in fact , When in javascript Use in css This is strongly recommended at this time .

9 selector1 ~ selector2 : Brother selector

ul ~ p {
color: red;
}

Brother node combination selector with Adjacent selector Very similar , And then it's not that strict .ul + p The selector selects only those elements that are immediately following the specified element . And this selector , All matching elements that follow the target element are selected .

10 selector[title] : Attribute selector

a[title] {
color: green;
}

In the example above , Only choose to have title Attribute elements . Anchor tags that do not have this property will not be modified by this code .

11 selector[href="foo"] : Attribute selector

a[href="http://strongme.cn"] {
color: #1f6053; /* nettuts green */
}

The code above will put href The property value is http://strongme.cn The anchor label of is set to green , Other labels are not affected .
Be careful : We put the value in double quotation marks . So in use Javascript You should also use double quotation marks when you write . If you can , Try to use standard CSS3 Selectors .

12 selector[href*=”strongme”]   : Attribute selector

a[href*="strongme"] {
color: #1f6053;
}

It specifies strongme This value must appear on the anchor label href Properties of the , Whether it's strongme.cn still strongme.com still www.strongme.cn Can be selected .
But remember it's a very broad expression . If the anchor label does not point to strongme Related sites , If you want more specific restrictions , Use it ^ and $, Represents the beginning and end of a string, respectively .

13 selector[href^=”href”]  : Attribute selector

a[href^="http"] {
background: url(path/to/external/icon.png) no-repeat;
padding-left: 10px;
}

You must have been curious , Some sites have an outside chain icon next to the anchor label , I'm sure you've seen this before . This design will tell you clearly that you will jump to other websites .
It's easy to do with carats . It's usually used to identify the beginning of... In regular expressions . If we want to locate anchor properties href China and Israel http Label at the beginning , Then we can use code similar to the above .
Notice we didn't search http://, That's not necessary , Because it doesn't contain https://.

14 selector[href$=”.jpg”]  : Attribute selector

a[href$=".jpg"] {
color: red;
}

This time we use regular expressions $, Represents the end of a string . This code means to search all the image links , Or other links with .jpg At the end of the . But remember that this way of writing is not right gifs and pngs It works .

15 selector[data-*=”foo”] : Attribute selector

a[data-filetype="image"] {
color: red;
}

Back to the previous one , How can we select all the image types png,jpeg,’jpg’,’gif’? We can use multiple selectors . Look below :

a[href$=".jpg"],
a[href$=".jpeg"],
a[href$=".png"],
a[href$=".gif"] {
color: red;
}

But it says it hurts , And it's going to be very inefficient . Another way is to use custom properties . We can add an attribute to each anchor data-filetype Specify the type of image this link points to .

a[data-filetype="image"] {
color: red;
}

16 selector[foo~=”bar”]  : Attribute selector

a[data-info~="external"] {
color: red;
} a[data-info~="image"] {
border: 1px solid black;
}

This, I think, will make your little partner exclaim wonderful . Few people know this technique . This ~ Symbols can locate labels whose attribute values are space separated multi values .
Continue to use the second 15 That example , We can set up a data-info attribute , It can be used to set any space separated value we need . In this example, we will indicate that they are external links and image links .

<a href="path/to/image.jpg" data-info="external image"> Click Me, Fool </a>

After setting this flag to these elements , We can use ~ To locate these labels .

/* Target data-info attr that contains the value "external" */
a[data-info~="external"] {
color: red;
} /* And which contain the value "image" */
a[data-info~="image"] {
border: 1px solid black;
}

17 selector:checked : Pseudo class selector

input[type=radio]:checked {
border: 1px solid black;
}

The above pseudo class writing method can locate the selected single box and multiple box , It's that simple .

18 selector:after : Pseudo class selector
before and after These two pseudo classes . It's like every day you find creative ways to use them . They generate something around the selected tag .
When using .clear-fix Many attributes are used for the first time .

.clearfix:after {
content: "";
display: block;
clear: both;
visibility: hidden;
font-size: 0;
height: 0;
} .clearfix {
*display: inline-block;
_height: 1%;
}

The above code will fill in a blank space after the target tag , And then remove it . You have to put it in your cornucopia . Especially when overflow:hidden When the method doesn't work , That's what works .
according to CSS3 The standard stipulates , You can use two colons ::. And then for compatibility , Browsers also accept a colon . In fact, in this case , It's wise to use a colon .

19 selector:hover  : Pseudo class selector

div:hover {
background: #e3e3e3;
}

Needless to say , You must know it . It's official user action pseudo class. It sounds a little confused , Actually, it's OK . If you want to paint some color on the place where the user's mouse floats over , So this pseudo class writing method can do .
Be careful : The old version of IE It's just going to be added to the anchor a On the label :hover Pseudo classes work .
We usually use it when we add the bottom border when the mouse floats over the anchor link .

a:hover {
border-bottom: 1px solid black;
}

Expert tips :border-bottom:1px solid black; Than text-decoration:underline; It's a lot to look at .

20 selector1:not(selector2) : Pseudo class selector

div:not(#container) {
color: blue;
}

Take the opposite Pseudo classes are quite useful , Suppose we're going to divide id by container All but div The labels are all selected . Then the above code can do it .

Or I want to select all the tags except the paragraph tags

:not(p) {
color: green;
}

21 selector::pseudoElement  : Pseudo class selector

p::first-line {
font-weight: bold;
font-size:1.2em;
}

We can use :: To select part of a label , Like the first paragraph , Or the first word . But remember that it has to be used on block tags to work .

The pseudo tag is made up of two colons :: Composed of .

Locate the first word

p::first-letter {
float: left;
font-size: 2em;
font-weight: bold;
font-family: cursive;
padding-right: 2px;
}

The above code will find all the paragraphs on the page , And designated as the first word of each paragraph .

It is usually used to highlight the content of some newspapers .

Locate the first line of a paragraph

p::first-line {
font-weight: bold;
font-size: 1.2em;
}

Follow ::first-line be similar , The first line of the paragraph is selected .

For compatibility , Previous versions of browsers were also compatible with the single colon notation , for example :first-line,:first-letter,:before,:after. But this compatibility doesn't work with the newly introduced features .

22 selector:nth-child(n) : Pseudo class selector

li:nth-child(3) {
color: red;
}

Remember the time when we had no place to start when we were faced with how to get the first few elements of a stacked label , With nth-child Those days are gone forever .

Please note that nth-child Accept a shaping parameter , And then it's not from 0 At the beginning . If you want to get the second element, then the value you pass is li:nth-child(2).

We can even get several sub tags defined by variable names . For example, we can use li:nth-child(4n) Go every other day 3 One element gets a label .

23 selector:nth-last-child(n) : Pseudo class selector

li:nth-last-child(2) {
color: red;
}

Suppose you're in a ul There are tags in the tag. N Many elements , And you just want to get the last three elements , Even so li:nth-child(397), You can use it. nth-last-child Pseudo class to replace it .

24 selectorX:nth-of-type(n) : Pseudo class selector

ul:nth-of-type(3) {
border: 1px solid black;
}

Only a short while ago , We don't want to choose child nodes , You want to choose according to the type of element .

Imagine having 5 individual ul label . If you just want to decorate the third one , And you don't want to use id attribute , Then you can use nth-of-type(n) Pseudo class , The code above , There's only a third ul The label will be framed .

25 selector:nth-last-of-type(n) : Pseudo class selector

ul:nth-last-of-type(3) {
border: 1px solid black;
}

Again , It can be used in a similar way nth-last-of-type To get tags in reverse order .

26 selector:first-child : Pseudo class selector

ul li:first-child {
border-top: none;
}

This structural pseudo class can select the first sub tag , You will often use it to remove the first and last border .

Suppose there is a list , Each label has a top and bottom border , So the effect is that the first one and the last one will look a little strange . At this time, you can use this pseudo class to deal with this situation .

27 selector:last-child : Pseudo class selector

ul > li:last-child {
color: green;
}

Follow first-child contrary ,last-child Take the last label of the parent label .
for example
label

<ul>
<li> List Item </li>
<li> List Item </li>
<li> List Item </li>
</ul>

There's nothing here , It's just one List.

ul {
width: 200px;
background: #292929;
color: white;
list-style: none;
padding-left: 0;
} li {
padding: 10px;
border-bottom: 1px solid black;
border-top: 1px solid #3c3c3c;
}

The code above will set the background color , Remove browser default inner margin , For each li Set borders to highlight a certain depth .

28 selector:only-child : Pseudo class selector

div p:only-child {
color: red;
}

Tell the truth , You'll find that you rarely use this pseudo class . However , It's quite useful , You don't know when you'll use it .

It allows you to get the child tag under the parent tag that has only one child tag . Like the code above , With only one paragraph label div It's colored .

<div><p> My paragraph here. </p></div>
<div>
<p> Two paragraphs total. </p>
<p> Two paragraphs total. </p>
</div>

In the example above , the second div Will not be selected . Once the first one div There are several subparagraphs , Then this doesn't work anymore .

29 selector:only-of-type: Pseudo class selector

li:only-of-type {
font-weight: bold;
}

Structural pseudo classes are smart to use . It will locate only one target of the same sub tag under a tag . Imagine you want to get a single child tag ul Label under li What about the label ?

Use ul li Will pick all li label . It's time to use only-of-type 了 .

ul > li:only-of-type {
font-weight: bold;

Finally remember : Use something like jQuery While waiting for tools , Try to use native CSS3 Selectors . It might make your code run fast . So the selector engine can use the browser native parser , Not your own .
If there are other students to nth-of-type And nth-child My understanding is still unclear , You can move to In depth understanding of css3 in nth-child and nth-of-type The difference between This article .

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