Which theme are you using? From the CSS alone it looks like there’s a fullwidth template. I gather there might also be a template with a sidebar. Try by going to the admin panel in the pages section, select the page you want the sidebar in, and see if in the drop-down list with the available templates for the page you can find one that might include a sidebar.
Sorry, I’m using twenty twelve.
The template is front page template and it is a fullwidth template. I tried the home page template and that left me with a header and no content. No side bar template available.