If you like to give this a try:
1) launch Google Chrome.
2) Under the back and forward page direction there should be a link to "Apps". Click that. Reference in the image below as "1"
3) Then click "Web Store".
4) In the search store box type "theme creator" Reference in the image below as "2"
5) Install the app in the image below as "3"
6) Just follow the easy instructions and you are ready to go.
You can even share your themes with others if you like. If you like Lord of the Rings, Warcraft, or fluffy kittens, you can create your very own theme. Every feature is customizable. If you are having trouble finding an image, you can go to Google Images and look for ones that you like under wallpaper. If you have any questions let me know. Have fun and be creative.