One thing I always loved about Opera was the customization options. I'm referring to the way it looks and not addons/extensions. When Opera 15 came out everything was gone. They didn't even allow the bookmarking of pages. But gradually over time some of the options came back. I usually like to put a background picture on Opera but the speed dials make it a fruitless venture because they usually cover the entire page.
Up to version 28 you could at least you could make the speed dials two columns and make the tiles smaller but then came version 29. They are like Microsoft, they either keep moving features around or remove them entirely. So now we are stuck with 3 columns and no resize not directly anyway.
I did find a way to adjust them, to make them bigger or smaller so that the chosen background picture will show through.
In the very top left hand corner of the browser, click on the red O. And in the menu that drops down look for the Zoom option. Click on the - symbol(minus sign or dash) before the 100% to zoom out or make everything smaller. The smallest is 25% or zoom in by clicking on the + sign (plus) to make them larger. It goes up to 500%.
That's alls to it. I was aware you could zoom in and out of a web page but I admit I did not realize it could be used on the speed dials. The zooming in and out does not effect the background picture size.
It just seemed pointless to me to be able to put in a background picture but then have it completely covered by the speed dials.
The zooming doesn't change the picture size but it will change the size of the Settings panel when opened. Also when you are zoomed in or out you will notice a new icon at the right end of the URL or address bar. A magnifying glass with a minus or plus sign in it. Clicking on it will open a little menu and give you the same option of zooming in or out. It also has a Reset button - resets to 100%.