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
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If you were upgrading the legacy app to our new one, you might have run into the error below while trying to authenticate. We're still investigating the cause of this but here's a workaround...
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