Making the left border narrower

When I go to the main viewing pages there is a very broad left border ( about a third of the page ), and I want to make this border narrower so that the main writing and reading part, ( to the right of the page ) is wider and allows for more text per line.

Hello Papaumau,

Can you provide a screenshot of the issue you'd like resolved? Thanks.

Tip: How to take a screenshot.