Not all fonts are suitable, but cannot be determined in the preview
When setting the fonts in Grub Customizer, the preview does not indicate if the special characters (lines, corners and arrows) will display correctly.
Please would you add to the preview a section of the lines and corners, and the up- and down-arrows.
I am attaching a screen-shot to show the two areas to which I am referring.
This would help to determine whether or not the font is suitable.