So I have a website, and by default everything is jammed to the left of the screen. With a different text editor I was able to add a margin to it of 300 pixels.

On most websites when you see the margin if you resize the website the margin disappears while the content stays the same. However on mine it just smashes everything and leaves the margin the same. What avenue should I go down to correct this issue?

Little more detail we are using a custom theme we bought, though not really sure why we are using it as I have stripped everything out and made my own look anyway. But removing it now would break everything I am assuming. The website is not live I am trying to build it for live.