Marks this element as being fixed to the top edge of the screen
using position: fixed.
When following a fragment link, the viewport is scrolled
so the targeted element becomes visible. By using this attribute you can make
Unpoly aware of fixed elements that are obstructing the viewport contents.
Unpoly will then scroll the viewport far enough that the revealed element is fully visible.
Instead of using this attribute,
you can also configure a selector in up.viewport.config.fixedTopSelectors.
Example
<div class="top-nav" up-fixed="top">...</div>
