feat: implement global styles for content headings

[duynguyen]

Fix #405

Test URLs:

• Before: https://main--danaher-ls-aem--hlxsites.hlx.page/
• After: https://405--danaher-ls-aem--hlxsites.hlx.page/

[aem-code-sync]

Hello, I'm the AEM Code Sync Bot and I will run some test suites that validate the page speed.
In case there are problems, just click the checkbox below to rerun the respective action.

• Re-run PSI Checks

[aem-code-sync]

Page	Scores	Audits	Google
/

[davenichols-DHLS]

Looks good, not sure if there are specific pages to check, but this is a global change. Thanks.