!important

#side { border: 1px solid #789; }
#side div { border: 1px solid #789; margin-left: 1em; }

H2: Lorem ipsum

Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Fusce at purus in diam tristique feugiat.

Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Fusce at purus in diam tristique feugiat.

H3: amet

Pellentesque congue malesuada quam.

Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia Curae;

Pellentesque congue malesuada quam.

Donec sit amet elit.

Nam suscipit consequat dolor. Donec sem.