Idea of CSV Icon
There is a square with the top-right corner appearing as it is folded downward towards the center of the square. Inside of the square, represents the three letters C, S, and V. All three letters are the same size and are in the order CSV.
This page shows the different variations of the CSV from an Icons8 icon pack. Feel free to resize and recolor the icon, and then download the icon in PNG format for free.