That's correct! those features are not available on Confluence cloud.
From the Functional differences in Confluence Cloud page:
On Atlassian Cloud, Confluence uses a custom theme that can't be modified or updated using custom HTML or CSS. For more information on custom themes in Confluence Cloud, refer to Working with Themes
Have you further questions relate to this topic?
Take our 5-minute survey to win a $500 Visa gift card! Are you currently using Confluence Cloud? We want to hear from you! Fill out this quick survey about your Confluence Cloud experience so we ...
Connect with like-minded Atlassian users at free events near you!Find an event
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no Community Events near you at the moment.Host an event
You're one step closer to meeting fellow Atlassian users at your local event. Learn more about Community Events