1.The background can not be too conspicuous in case it should compromise the legibility of the foreground content. Environment art or ambient art is recommended.
Correct
Image should not be too highlighted because it hinders the reading of foreground content.
2.The two sides of the top image gradually change into pure black and the edge of background into another pure color.
Correct
The two sides of the top image do not gradually change into pure black. The edge of background does not gradually change into a pure color.
The gradience does not look natural and the image is torn apart by this fault.