Sheets: It is spread on the bed. If the sheets have rounded corners, they will look very good, and the corners of the sheets are not easy to rub on the ground. Disadvantages: If the mattress underneath is very slippery, it is easy to wrinkle if you are not sleeping well, and the bed sheet is easy to slip, and you need to take care of it frequently to keep it tidy. Bed cover: There is an elastic band around it, which is equivalent to a cover on the mattress. If it is tucked under the cushion, it will not slip off easily.