When downloading icons or illustrations, paying attention to their file format and their size is important for the item to look good.
If you are downloading files in PNG and they look blurry or pixellated, try downloading the largest size instead (512x512 px).
If you want the item in a larger size, download the SVG format instead. The SVG (vector) allows you to resize the file infinitely without it losing quality.
For more detailed information about file formats, please check What file format is suitable for your intended use.