How to understand weights and cascading rules determines the priority of CSS style.
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The code is as follows:
# redP p {
/ * weight = 100,116,101 * /
Color:#F00; / * Red * /
}
# redP .red em {
/ * weight = 100mm 101m 111 * /
Color:#00F; / * Blue * /
}
# redP p span em {
/ * weight = 100 "1" 1 "103 * /
Color:#FF0;/* yellow * /
}
Red
Em red
Red
1. Basic priority rules
Compare the number of the same level, the more the priority is, if the same is the same, that is to compare the number of the next level, as for the priority of each level is as follows:
Important > inline > ID > Class > tag | pseudo class | attribute selection > pseudo object > wildcard > inheritance
II. CSS weight rules
In "Modular Design in Page Refactoring," it is mentioned that there are two important factors that affect the weight of CSS styles:
A: the priority of styles is related to the order in which styles are defined.
B: the size of the weight is related to the type and number of selectors
In general, if there are two styles with the same name in the same CSS file, the later defined will overwrite the first defined. For the priority of the selector type, see (1).
So, how is the weight of CSS calculated?
A selector weight representation: 0.0.0.0, according to the calculation rules to fill each number, the corresponding position is equal, then compare the next bit.
The rules for calculating the weights are as follows: (for convenience, replace the values of each position with A.B.C.D)
1. Inline style: Achim1je Bauer Centro (I. e. 1.0.0.0)
2. ID style: if there are several ID in the selector, add a few 1s in the second bit, such as # header {color:red}, that is, the Aging Craft Depend0Basil (i.e. 0.1.0.0)
3. The number of classes, pseudo-classes, and attributes is the third-digit value:
.a.b [type= "text"]: hover {}, there are two classes, one attribute and one pseudo-class in the selector, so its third bit is 4, which is named as 0. 0.4.0.
4. The number of pseudo elements and tag elements is the value of the fourth bit.
P:first-letter, which has a tag element p and a pseudo element first-letter, with a value of 2menagram Bamboo Category 0Didence 2 (i.e. 0.0.0.2)
5. Wildcards and inherited CSS attributes have no effect on weights.
Third, a few examples
For the above, take a look at the following examples
1. A. B.C {color:red;} / / 0.0.3.0 description: there are only three classes
2. * {. } / / 0.0.0.0 description: wildcards have no effect on weight
3. A. b a {color:green} / / 0.0.2.1 description: two classes and one label
4. # hid {color:black;} / / 0.1.0.0 description: there is only one ID
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