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Share a detailed introduction to the style override principle in CSS
- 黄舟Original
- 2017-07-22 10:58:171414browse
Rule 1: When a style conflict occurs due to inheritance, the nearest ancestor wins (The nearest principle).
The inheritance mechanism of CSS allows an element to inherit styles from the ancestor elements that contain it. Consider the following situation:
<html>
<head>
<title>rule 1</title>
<style>
body {color:black;}
p {color:blue;}
</style>
</head>
<body>
<p>welcome to <strong>gaodayue的网络日志</strong>
</p>
</body>
</html>strongFrom body and The color attribute is inherited in p, but since p is closer to strong in the inheritance tree, the text in strong eventually inherits the blue color of p.
Rule 2: When the inherited style conflicts with the directly specified style, the directly specified style wins (The most direct principle).
In the above example, if the style of the strong element is also specified, such as:
strong {color:red;} Then according to rule 2, the text in strong will eventually be displayed in red.
Rule 3: When directly specified styles conflict, the one with the higher style weight wins.
The weight of the style depends on the style selector. The weight is defined in the following table.
css selector weight
Label selector 1
Class selector 10
ID selector 100
Inline style 1000
Pseudo element (:first-child, etc. ) 1
Pseudo class (:link, etc.) 10
As you can see, the weight of the inline style>>ID selector>>Class selector>>Label selector , in addition, the weight of the descendant selector is the sum of each weight, for example, the weight of "#nav .current a" is 100 + 10 + 1 = 111.
Rule 4: When the style weights are the same, the latter wins.
Consider the following situation
<p class="byline">Written by <a class="email" href="mailto:jean@cosmofarmer. com">Jean Graine de Pomme</a></p>
.byline a {color:red;}p .email {color:blue;}".byline a" and "p .email" both directly specify the a element above, and both have a weight of 11 , according to rule four, the final display is blue.
Since style sheets can be external or internal, Rule 4 reminds us to pay attention to the order in which external style sheets are introduced (and the order of 2cdf5bf648cf2f33323966d7f58a7f3f elements), as well as external style sheets and internal styles. The position where the table appears. Generally speaking, internal style sheets appear after the introduction of all external style sheets, usually before 9c3bca370b5104690d9ef395f2c5f8d1.
Rule 5: !important style attributes are not overridden.
!important can be seen as a "golden finger" to break the above four rules when it is absolutely necessary. If you must use a certain style attribute and prevent it from being overridden, you can add !important after the attribute value. Taking the example of rule 4 as an example, ".byline a {color:red !important;}" can Force the link to appear red. In most cases, style overrides can be controlled in other ways, and !important cannot be abused.
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