Unable to add new plugins

Hello!

Really hope you can help with a small issue I am having. While working on a child theme I have added the following code to child’s style.css

/* no page titles */

.page .entry-header {
	display: none;
}
.page .entry-content h2 {
	margin-top: 0;
}

Since then every time I try to add new plugins I get the following message:

An unexpected error occurred. Something may be wrong with www.remarpro.com or this server’s configuration. If you continue to have problems, please try the support forums.

If I remove above code from style.css everything works fine?

Any help would be much appreciated.