Limiting Characters in custom box

[JANA21]

Hi 

I hope I have put this is the correct section. I have searched the internet with no success. 

I have successfully added code to create customise boxes, but I can not work out how to limit how many characters they can put in the box. 

I did find a solved post on here, but when I have tried it, it is not limiting it. 

I'm starting to wonder if I should just pay $49.99 per month for an app instead of making templates and sections for different variants, even if I do work out how to limit characters. 

[KetanKumar]

@JANA21 

do you mean like this?

https://www.w3schools.com/tags/att_textarea_maxlength.asp