Header area CSS ID

Hi there, I have the following question - where/how can I add a CSS ID associated with a json code to slightly change the appearance of the header area?
Thank you

This is for the Rocked theme btw

Hello there,

I am sorry, I’m not sure about the JSON code to modify the header area. Have you checked the theme’s header.php file where the main header is defined? See this code block:

<header id="header" class="header">