Can not save background-image style in multiple lines of text column ?

Hi all,

I created a custom list, after that I created a column "multiple lines of text" with "Enhanced rich text". After that, I created a new item, and I input html source to that column.

ex: 

<div style="background-image:url('/_layouts/15/images/itwp.png');background-repeat:repeat;width:100px;height:100px;"></div>

I saved that item, when I open it, background-image style was removed. Please help me.

thanks so much,

Aladinsg