If you want to change the background theme in Opera, or create your own, do the following:
Right-click on the Speed Dial page and choose Change theme. Here you have some choices. Default themes, My theme, Get more themes, Go to start page.
Default themes are the ones built into the browser. Get more themes sends you online where you can download and install more themes. My themes shows you the ones you’ve created, which leads us to Create your theme.
Create your themes gives you the opportunity to use your own background pictures or designs. Just click on it then click Choose file. Find a picture on your computer to use as a background on the Speed dial page. Keep in mind the speed dials themselves are going to obscure most of the background picture which almost makes it pointless (one of my reasons for sticking with version 28).
You have some control over the alignment of the picture by clicking on the Bottom, Center, or Top icons. Experiment to see which suits your purpose. You can select the text color and add a Text shadow, then click on the Create button.
These will then appear in your My Themes section. Just go through your list and pick one by clicking on it to set it as your theme. If you want to delete a theme just move your mouse over one and in the bottom right-hand corner you’ll see a small circle with a white x in it. Click on this and confirm that you want to delete. And that’s it.