css - parent's position is absolute and child&

问题:

I have div which hosts another div. Ok, I get the case when the parent is position:relative and the child is position:absolute. I don't get what happens when

1. parent's position is absolute and child's position is relative
2. parent's position is absolute and child's position is absolute
3. parent's position is relative and child's position is relative

I use the JSbin example from Why does an absolute position element wrap based on its parent's right bound? but the question applies to positioning concept in general

回答1:

Read more about absolute, relative, and fixed position and how they differ here, but I'll try to answer your question about relationships specifically.

position: absolute will position that element to it's nearest parent with a position other than static. Static is the default for everything.

position: relative is a little weird because it really affects that element's children, not it's own position. It's just saying to it's child elements, "position yourself relative to me if you have position: absolute." A position of fixed or absolute does the same thing (meaning its positioned children will position themselves relative to its boundaries), but these styles also affect their own position on the page. An element with position: relative won't look any different, but it's children might.

So consider a situation like this:

<div class="parent">
     <div class="child">
           <div class="grandchild"></div>
     </div>
</div>

If grandchild has position: absolute, it will position itself relative to the browser window because there is no parent with a position other than the default of static.

If parent also has position of relative, absolute, or fixed, grandchild will position itself relative to the boundaries of parent.

However, if child also has a position of relative, absolute, or fixed, the grandchild will position itself relative to child's boundaries, because it is the nearest parent with a position other than static.

In summary, relative affects an element's children, while absolute and fixed affect the element itself as well as its children.

And remember that position: fixed bypasses all relative and absolute parents and always positions itself relative to the browser window.

回答2:

1 - if the mommy is relative and the child is absolute : the mommy listens to her child. as if to protect him. sort of.. 2 - if they are both absolute : they have nothing to do with eachother. they are strangers to eachother. 3 - if the parent is absolute and child relative : they are bound. the child moves ( width and height ) towards or away from his mommy.

It will always be a little strange, there are a lot of great texts about this, but also for me it is always just switching absolute and relative until it works. hope this cleares it up a little.