Code in parent theme not working in Child theme

I want to add the sidebar to all post pages on Duster. I’ve got the sidebar to appear by adding it to single.php but cant get the page aligned in my Child theme.

Adding the following code to my parent theme’s style.css aligns the page perfectly… however it doesn’t seem to work for my child theme when either adding it directly to the child theme’s css or leaving it in the parent theme and letting the child theme inherit it. Any suggestions?

#primary {
	float: left;
	margin: 0 -26.4% 0 0;
	width: 73%;
}

.singular #content {
	margin: 0;
	position: relative;
	width: auto;
}

#content {
	width: 86.4%;
}