Run adds guardrails to the choices our users can make in order to help ensure that Run sites looks consistently good, and on all screen sizes.
One of those guardrails is a character limit that we add to a variety of text fields on the site. The character limit varies by text field, but you'll notice that either you can't type past a certain point, or that text you paste in gets truncated at the character limit.
Users can disable character limits across their whole site, by flipping the toggle provided at the bottom of the Site Settings page.
If your character limits are disabled, make sure to do additional testing of your site on mobile to make sure it looks good at all screen sizes.