Take a look at this tutorial: Creating Fixed Headers with CSS
But from a strategic perspective, curious of this time investment. My assumption is that you are building a landing page to capture information, possibly from a paid marketing effort. I would first focus on creating a landing page designed to convert...then worry about small things like this that won't move the needle much at all. Marketo has some okay responsive templates. Knak and Unbounce are great if you have a bit of budget it spare. Unbounce, while the most expensive, could likely get you a well converting landing page with the ability to match your branding (and fixed header).
Thank you for your advice !
Of cource, I know this small things don't influence to capture information, but I want to try this system.
I don't have skills of CSS and HTML, so I'll try Knak or Unbounce.
Don't make a quick decision w/Unbounce based only on looks. If you don't integrate Unbounce correctly with Marketo, you will lose vital tracking information (hint: do not use their native Marketo "integration").
We are using Unbounce for our LPs and used the native Marketo integration. We've gotten multiple 609 and 610 errors since integrating but can't figure out what the exact problem is. How do you suggest to integrate Unbounce and Marketo?
I have some posts about it in the Community. In essence you must turn off their REST-based "integration" and use Marketo's forms endpoint.