remove "posted by" via jetpack for Twenty Ten

Hi there,
My Front Page is set to blog, but I don’t want all that stuff saying posted by, in etc.

I read on a previous forum post to put this in jetpack css edit.

.entry-utility {
	display: none;
}

I did this but it made no difference. I also tried something similar under the content section of style.css , but again – it made no difference.
Can anyone help?
(I know Twenty Ten is a bit old, but it generally does what I want at https://www.htth.org.uk)
Thanks,
Richard