Fixed Header hidden on JQuery Steps page (only on certain mobile browser)

I can't seem to get my header to display on the page where the jquery-steps form are displayed. And this only happens on certain mobile browser such as the 360Browser(v1.1.0) and also the WeChat Built In browser.

I don't have any clue what might be wrong here so any help guys?

My test website is at m.demo.rsi.sg. To get to the page, simply select any items (total checkout value must be > 40) and then proceed to checkout and click sign up.

Am nearly going bonkers over this - any help would be appreciated, thanks!

Solution

<div class="header">
   <div class="logo"></div><div class="menu"></div>
</div>

<style>
    .header{position:fixed;
            top:0;
            z-index:2;
           }
</style>