website header and browser bar disappear when scrolling down

I designed my website using your beautiful Woodmart template. i designed this page for browse categories by mobile version :
http://www.medshow.net/category

However, when I scroll down to the bottom of the page, both the site header and the browser bar disappear. I would like the site header and the browser bar to remain fixed when scrolling down to the bottom of the page.

I read that this issue can occur for users when browsing the website through certain browsers, especially mobile browsers. However, I noticed that in my old site, which I used a different template for, this problem does not appear when I browse my old site with the same browsers.