as it seems, you are right. If i use the following code:
filter: url(“data:image/svg+xml;utf8,<svg xmlns=\’http://www.w3.org/2000/svg\’><filter id=\’grayscale\’><feColorMatrix type=\’matrix\’ values=\’0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\’/></filter></svg>#grayscale”);
it just works out perfectly!
Could be a possible solution for most people facing the same problem.
edit: as i am not so much into coding, i have to admit i got that piece of code from here
