trouble finding what css I’m using :(

Sorry, but I’m sure everyone knows this answer but me.

I have downloaded and am using a theme that works well for me. Now, I want to create and edit my postings outside of wordpress. I find that if I point my css at:

<link rel=”stylesheet” href=”https://mydomain.net/blog/wp-admin/wp-admin.css?version=1.5.1.2&#8243; type=”text/css” />

my http viewer from non-wordpress works fine.

Two questions:

1. Where style sheet should I download to my PC will work the same as the above?

2. What style sheet do I add to? I’ve tried the “theme editor” but changes in that don’t seem to affect my page.

Thanks, -Peter