Detailed explanation of several common CSS selector examples

Methods to import external css style sheets

Use the link tag to import external css style sheets

Import (import) external style sheets in the style sheet

@import url("/crazy-html5/06css/css/demo01.css");

Use internal style sheet

The internal style sheet can only be applied to a certain web page. The definition method is to add the style tag in the head header. You can add it in the style tag. Page style.

Selector knowledge points

Element attribute selector

1) Ordinary tag selector

table:{background:red;}

2) A tag containing a certain attribute

p[id]{background:red;} represents a p element containing an id attribute

3) A tag that contains an attribute and the attribute value is a specific value

p[id=aaa]{background:red;} represents a p element that contains the id attribute and id=aaa

4) Elements that contain an attribute and the attribute value starts with a specific value

p[id=^aaa]{background:red;} means that it contains an id attribute, and the id value starts with aaa p element

5) An element that contains an attribute and the attribute value ends with a specific value

p[id=$c]{background:red;} means that it contains the id attribute, and the id The value is a p element ending in c

ID selector

id selector, specifying the element whose id is a specific value, for example, #myp means that the id is myp For elements with a value, the symbol

#Class selector must be added in front of the id selector. The class selector is an element that matches the class value. The symbol must be added in front of the selector. , for example, .myclass represents all elements whose class value is myclass.

Contains selectors and descendant selectors

The descendant selector can select elements that are descendants of an element, for example: h1 em{color:red}, this rule will Turn the text of the em element that is a descendant of the h1 element into red. Other em text will not be affected by this rule.

Child selector

is similar to the descendant selector, but will only act on certain direct descendants of the element. For example, h1>strong{color:red;} acts on the first-level strong element in the h1 element, and other levels are not affected

Adjacent sibling selector

If you need to select an element immediately after another element, and both have the same parent element, you can use the adjacent sibling selector, such as h1+p{margin-top:50px;} to select the element immediately after h1 In the paragraph that appears, h1 and p elements have the same parent element

Selector grouping

Selectors that act on multiple elements at the same time, such as h2, p{color :gray;} will affect both the h2 element and the p element.

Pseudo element selector

1): first-line{color:red; }Set a special style for the first line of text

p:before{
    content:url("img.png");
}

after and before can be used with quotes, quotes can be used with the quotation mark type for setting nested references

You can use a counter to add multi-level numbers in front of the text. This can be a special article and will not be detailed here.

Pseudo-class selector

1 :root selector matches the document root element

Pseudo-class selector for element status

1 :hover Style when the mouse pointer is on the element

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