Hi @Nate Gervenak,
I would recommend you to use SharePoint Framework (SPFx) Extensions to apply the css for all pages. This solution helps to add/modify/delete custom js and css file references using SPFx application customizer extension all modern pages within SP online site. You could deploy the extension to your page to manage your css style.
https://github.com/pnp/sp-dev-fx-webparts/tree/main/samples/react-add-js-css-ref
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