How to overlap one block with another?

Question

css

There is a structure:

<div>
    <div class="a">Контент</div>
    <div class="b">Блок, который затемняет его</div>
</div>

How can I make the block with class b occupy the entire area of ​​the parent and darken the A block.

Answer 1

Set the big block to position relative.
Set the b block to absolute and set the height and width to 100% or top, right, bottom and left to 0.

Answer 2

z-index. This property only works on elements that have their position set to absolute, fixed, or relative. Syntax: z-index: number;