CSS changes not taking effect in customized styles folder
Make the changes to the style.css file which is in Jackson theme folder. Not under mytheme


Use

#banner-wrap {
background: transparent url(../images/main-sprite.png) repeat-x scroll center -90px !important;
height: 133px !important;
overflow: hidden !important;
width: 100% !important;
}

Add this in to style.css file
Flush the cache once.