how do i make 2 hor lines under menu bar?

Hi there,

Can anyone pls tell me how to make two horizontal lines under the Menu bar? One of my pages is displaying it properly, like this.

http://bigscreenhire.com.au/screen-rental/

However, the rest of the other pages have only one line across like this:

http://bigscreenhire.com.au/

Thank you.

bigscreen