Accessing content variables through the page variable
Per the docs on the core page.html.twig:

 \* Page content (in order of occurrence in the default page.html.twig):
 \* - messages: Status and error messages. Should be displayed prominently.
 \* - node: Fully loaded node, if there is an automatically-loaded node
 \*   associated with the page and the node ID is the second argument in the
 \*   page's path (e.g. node/12345 and node/12345/revisions, but not
 \*   comment/reply/12345).


The node variable is available in page.html.twig. If you need to access one its fields you can use {{ node.field_myfield.value }} to print it out.