Need help with css script for background header

site url http://mf648animes.tv

Css script for header

#header {
   background:url(https://dl.dropbox.com/s/hhawtz1iz1nj5ez/ani10.gif) no-repeat center;
}
 
#undertop {
   background:#c8e2ef url(https://dl.dropbox.com/s/lcw9ewh3pg8l9ow/ani10sub.gif) no-repeat top;
}

Code (markup):

Same Script alternate location

#header {
   background:url(images/headers/ani10.gif) no-repeat center;
}
 
#undertop {
   background:#c8e2ef url(images/headers/ani10sub.gif) no-repeat top;
}

Code (markup):

i need these two gifs to play at the same time only when both have fully loaded

what do i do to make that happen?
Please do not edit the script just tell me what to add to the script as this script is designed for the header i have
links to the images are



<img src="http://mf648animes.tv/wp-content/themes/anime-visual-theme/header10.css">