I will show you guys how to make smooth background!
Drag out a red Set Position block. Inside, type 0 into the X and Y spot.
Drag out a blue Repeat Times block. In the space, write 1024.
Drag out 2 purple Leave a Trail blocks, and put them in the Repeat Times block.
Drag the red Move Forwards blocks inside the purple Leave a Trail blocks outside where the code is, and to where all of the blocks are.
Change the trail widths to 1, and choose any colors you want, just not the same color.
Drag out 2 red Set Position blocks, and put one in each purple Leave a Trail block. In the first Y spot, put 800, and in the second Y spot, put 0.
For the firs X spot, tap the bubble, and drag in the addition (+ symbol) block into the first X spot. For the first + spot, go into values and select Text X Position. For the second + spot, type in 1. The next X spot is simpler, just drag out another Text X Position and put it in the second X spot.
Watch your glorious smooth background play out! Thanks for @Kiwicute2015 for the coding.