Append DIV (specified by class) inside other DIV (specified by other class)

Append DIV (specified by class) inside other DIV (specified by other class)

I have HTML sheets "A" and "B". (HTML sheet "B" is read into html sheet
"A". "A" works as a "template" for the very varying content in "B".)
I have this div in HTML sheet "A".
<div class="productsheet-container">
</div>
I add this div to HTML sheet "B":
<div class="productsheet">
hello
</div>
This is my required outcome:
<div class="productsheet-container">
<div class="productsheet">
hello
</div>
</div>
The div class="productsheet" should be hidden from its original position.
So only be visible inside div class="productsheet-container".
If anyone could help me here, I'd be forever grateful! What JavaScript do
I use exactly? Note! I'm a COMPLETE NEWB to JavaScript, haven't written
one single line in my life! So, to me, the answers I've found googling
seem insufficient.
I've, for example, tried:
$( ".productsheet-container" ).append( $( "<div class='productsheet' />" ) );
But shouldn't I write something before and/or after too?