responsive web design - mobile and desktop

What are you most proud of, and what would you do differently next time?

I am proud I nailed it. It took much more time than I expected because had some problems with the picture. Now I know one of the ways to do that and just added two 's with for every design and added two classes for them. Next I applied display: block/none dependently on the design. But I am really open for suggestions. If someone knows a better way to to it faster/better - just write a comment. I'll be grateful.

What challenges did you encounter, and how did you overcome them?

As I wrote the biggest challenge was adding pictures for every design, because the background-image does not work, and I don't know why. So I must give up much time to resolve the problem and make that pictures displayed properly. I just added two img's to the html file, and two different classes with using display: block/none for them. Next challenge was when I tried to apply Responsive Web Design, and arrange all the elements in my project. Sometimes, when you want to arrange the desktop/tablet/mobile - something in the other one can break and you still need to check others designs to fix bugs online.

What specific areas of your project would you like help with?

I am just looking for a better way to add images for every design in a proper way. I'll write it again. The background-image did not want to work today, and I do not know why. I managed to do it, but maybe someone wants to share a better way with me.