How do you make a <div> appear inside a parent <div> ?

Question

I have been trying to make a <div> appear inside another one. As we all know, <div>s are block level, so they tend to appear below each other. anybody got an idea?

Answer 1

Couldn't you just put a div inside the other one?
https://code.sololearn.com/W61zN4ofOIR8/?ref=app

Answer 2

thanks for your answer but this is actually what i meant:
<div class="wrapper">
<div class="a"></div>
<div class="b"></div>
<div class="c"></div>
<div class="d"></div>
</div>
I want "d" to appear infront of "a" "b" and "c"

Answer 3

use CSS z-index