How to make an added note a required field on Shopify?

[mj246]

I want customers to enter a note before checking out at our store. I have the note customized but want it to be/say "required field" before they check out. How can I accomplish this?

[PaulNewton]

Add the required attribute to the html input.

Thought without also writing validation rules this can just mean people have to enter a single character to proceed.