Is there a way to style the main-container without it effecting ALL the site?
You can do it using the CSS. First on whichever node you want to do, find its specific class given when you create that node (How: right click on the page and Inspect element in the code ........., you will find the several class, one of which is specific for that node). Now take that class. Now suppose if you want to change the main-content with that node only and do not want to change other, use following selector in css,

.specific-page-node-class #main-content {your css code}


This will apply change to main content of that specified node only and do not change to other.

Credit: Link for detail question and answer which I asked on same topic on the Drupal answer, I have summaried above