Thanks! I just do these things that list?
1) create a file fontsize.css and I put it in my child theme.
2) take the file custom-fontsize-css.php, I put it in a folder and load it via ftp in the folder plugins.
3) the active and I can use the file fontsize.css to make my changes.
I only have one doubt. The folder I have to upload via FTP plugin, must contain only custom-fontsize-css.php and nothing else?
