How to Remove "Block Borders"

I have Dolphin 7.2.1

I put some custom HTML blocks in certain pages.
I wanted to remove the heading and the block outline and display ONLY the content inside some of the blocks.

NOTE:

I do not want to remove the outline and heading from all  the blocks.
I want to remove the outline and heading from only a few blocks.

Basically, I have image banners inside these blocks and it looks very awkward when you see a heading and a surrounding outline around a banner.

I know it can be done by changes to certain record values in a particular table.

Which table and what field?

Any suggestion will be appreciated.
 

every block has id, use css to eliminate the borders like this:

#blockid445

{

border:none;

}