Possibility to add form on top of grid.

Dear community,
I have a div that pops up in the middle of the screen when clicking a button one of the column’s rows.

The window pops up through a custom column:

this.setCValue("<div class='popup "+row_idd+"'><div id='myForm'></div></div><input type='button' class='popbut' name='"+row_idd+"'>",val);

So I tried to add a form through another form script on my page. But somehow it won’t show up. Just an empty popped up div.
Any clues?