CSS priorities and targeting specific elements

问题:

My question should be pretty strait forward. For some reason I can't wrap my head around it today.

I'm making a menu with a structure like so

<div class="wrapper">
    <ul>
        <li class="menu-item"><a href="#">Menu Item</a>
            <div class="inner">
                <a href="#">Login</a> 
            </div>
        </li>
    </ul>
</div>

I am trying to target the login link using the following css selector:

.inner a{}

The selector is working, however the following selector is taking css presidence, and overriding the above selector:

li.menu-item a{}

I'm totally baffled. Why would the second selector take style preference over the first? How would you guys recommend I target the above "a" elements?

回答1:

Why would the second selector take style preference over the first?

Because the second selector is more specific than the first. The first contains one class and one type selector while the second has one class and two type selectors.

To calculate specificity, think of an selector as consiting of four numbers, all starting at (0,0,0,0)

• Inline styles have the highest specificity and would take the place of the first number (1,0,0,0).
• ID's count as the second number (0,1,0,0)
• Classes, pseudo-classes (other than :not()) and attribute selectors count as the third number (0,0,1,0)
• Type selectors and pseudo-elements - e.g. div {} or ::after{} count as the fourth (0,0,0,1)

Also:

• The universal selector * has no effect on a selectors specificity.
• Combinators like +, ~ and > also have no effect on specificity.
• !important rules almost always take precedence; though they don't affect the four numbers associated with a selectors specificity. Only another !important rule can override a previously defined one. The exception is when the previously defined !important rule has a more specific selector. Here, the normal rule of specificity (described above) apply.

回答2:

CSS Selectors have a "weight" system attached to them,

• Element, Pseudo Element: d = 1 – (0,0,0,1)
• Class, Pseudo class, Attribute: c = 1 – (0,0,1,0)
• Id: b = 1 – (0,1,0,0)
• Inline Style: a = 1 – (1,0,0,0)

so your first selector has a score of (0,0,1,1) while your second selector has a score of (0,0,1,2) which is higher and thus takes precedence

回答3:

That is because li.menu a contains three parts to idendtify the element: the parent element (li), the parent class (menu-item) and the element (a). Your intended selector only has two, so you could modify it to this:

li.inner a{}

And it should work.

Edit:

I knew I'd answered this before: Why does my HTML not use the last style defined in the CSS?

回答4:

CSS precedence is won by the DOM object with the highest specificity.

So what earns specificity?

Element Selector -- 1
Class Selector -- 10
ID Selector -- 100
Inline Selector -- 1000

In your example: .inner a would be 11 points

a(1) + .inner(10) = 11

li.menu-item a is 12 points

li(1) + .menu-item(10) + a(1) = 12

So that's why the second will be what's shown. To make the correct style show, just make it more specific, for example use .menu-item .inner a

There's a very good article about this here. http://www.stuffandnonsense.co.uk/archives/css_specificity_wars.html

回答5:

You can apply the CSS only to the anchors inside each element, like this:

li.menu-item > a{}
.inner > a

Doing it this way, the rules of "li.menu-item a" will not interfere in the other anchor.