How to change font size in a textbox in html
For a <input type='text'> element:
input { font-size: 18px; }
or for a <textarea>:
textarea { font-size: 18px; }
or for a <select>:
select { font-size: 18px; }
you get the drift.
To actually do it in HTML with inline CSS (not with an external CSS style sheet)
<input type="text" style="font-size: 44pt">
A lot of people would consider putting the style right into the html like this to be poor form. However, I frequently make extreeemly simple web pages for my own use that don't even have a <html> or <body> tag, and such is appropriate there.