We do exactly this all the time!
Fun things to consider:
- Old Marketo templates referencing external CSS (non-mobile friendly) don't pull in external CSS into the WYSIWYG editor unless they're https calls. This breaks your WYSIWYG pretty considerably, but the approved pages look great.
- New Marketo templates (mobile friendly) referencing external CSS DO pull in externall CSS into the WYSIWYG, even as normal http calls.
- Expect the JS not to work in the WYSIWYG but be totally functional on the approved page.
- Custom fonts hosted on your WWW likely won't work on your Marketo-native pages in some primary browsers included Chrome. If you want those custom fonts to show, either use an external font hosting service or upload them to Marketo's Design Studio and change your CSS to reference these fonts. This is an issue with cross-domain font calls.
I usually do at least two external CSS references:
- The WWW stylesheet with all your normal branding
- A Marketo-specific stylesheet with Marketo-specific tweaks and branding.
Having a Marketo-specific stylesheet helps you not have to deal with your WWW site's development team and "will this have adverse effects on our primary domain" questions. There are also lots of really Marketo-specific tweaks that you'll have to make when you want to change things such as forms.
The order of where stylesheets/styling shows up in the landing page doesn't have much that you can change. Marketo likes to spit out lots of in-line CSS which becomes absurdly complicated to overwrite without really nailing the CSS hierarchy and slapping on some (awful webdev practice but unavoidable) !important attributes to your stylings.
Here's an example of using external CSS on this page. You can also see it's puking font errors in the Web Inspector Console. But that uses entirely external CSS on the page.
(And, like you mentioned, when your WWW site ever updates, it can unexpectedly break your formatting. When you're doing a new launch, usually the webdev team has Marketo landing page design as a low priority, so watch out for this ahead of time and know it's coming.)
Best,
Edward Unthank | Founder, Etumos