Css code to add "Last Updated on" after inserting php snippet

Hi, i followed other tips and Ive been able to set my posts to display the dates there were last updated. But I'd Like a CSS code to have "Last Updated on:" in front of the dates of older posts.

This css code stopped working after i added the snippet

.posted-on .updated {
display: inline-block;
}

.posted-on .updated + .entry-date {
display: none;
}

.posted-on .updated:before {
content: "Last Updated ";
}