I found the following code to add an input in my product theme which show up in the cart but I do not know how to change the size of the “box” (for ex the height) :
I’d recommend giving the free Easify Product Options app a try for adding a text field to your product pages. It’s a quick and straightforward process that will take just a few minutes . With this app, you can effortlessly select between a Text Box (for short text) or a Text Area (for longer text), and you’ll have access to a variety of useful settings like placeholders, help text, tooltips, and text length restrictions.