How do I change the length of a border in HTML

Question

I'm not trying to change the thickness. I need to make it so that a border doesn't touch the other side of a page (that's what it does by default) and I need it to touch the middle of the page if that makes sense. Basically I want to adjust the height and length of a border.

Answer 1

<style border ="10 px"></style>

Answer 2

please code like this