

What is CSS specificity?
<p> Specificity can be understood as the "priority" of a CSS rule. When multiple rules match the same element and the same attribute is set, the browser will compare their specificity and select the "strongest" rule to apply.
p { color: red; } #main p { color: blue; }<p> If the
<p>
element is in a container with id="main"
, then the second rule has a higher specificity and the text color will be blue. 
How is specificity calculated?
<p> Specificity is a four-digit number consisting of four different types of counts (usually written as a, b, c, d):- a : The number of inline styles (such as
style="max-width:90%"
) - b : The number of ID selectors (such as
#header
) - c : The number of class selectors, attribute selectors and pseudo-classes (such as
.class
,[type="text"]
,:hover
) - d : the number of element selectors and pseudo-elements (such as
div
,::before
)
For example:
Selector | a | b | c | d | Specific values |
---|---|---|---|---|---|
p | 0 | 0 | 0 | 1 | (0,0,0,1) |
p.error | 0 | 0 | 1 | 1 | (0,0,1,1) |
#main p | 0 | 1 | 0 | 1 | (0,1,0,1) |
style="color:red" | 1 | 0 | 0 | 0 | (1,0,0,0) |
Common misunderstandings and suggestions
<p> Many people think that using multiple classes can exceed the ID, but in fact it doesn't work. For example:#main {} .container.sidebar.highlight {}<p> The former has only one ID, and the latter has three classes, but the weight of the ID is much higher than that of the class, so the specificity of
#main
is still higher.
Some practical suggestions:
- Try to avoid using IDs to set styles, because they are too "strong" and easily make the style difficult to overwrite.
- Using class name combinations is easier to control hierarchy and is more conducive to reuse.
- If you find that a certain style cannot be covered, it may be because its specificity is too high, so you can use the browser developer tools to check it.
- Although
!important
can be used forcibly overridden, it should be used as little as possible because it will make debugging more difficult.
Let's summarize
<p> The specificity calculation is not complicated, but it is based on the "component analysis" of the selector structure, rather than a simple numerical summation. Understanding this mechanism can help you write clearer and more controllable CSS, and reduce unnecessary!important
and duplicate code.
<p> Basically that's it.The above is the detailed content of How is specificity calculated for CSS Selectors?. For more information, please follow other related articles on the PHP Chinese website!

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