How to add remove sub navigation bar and display them in main navigation?

[RoguePanda]

This image about shows the default display of navigation bar, when we are in some page, it shows the sub navigation bar. (red marked)
Now I want to hide the subnavigation, and always keep the default style of main navigation bar, with a single triangle right side.

Let's get some examples, hypixel.net.

No matter which page are you in, the navigation bar just shows in one line. I want to have the same effect, but how to do it?

Thanks for everyone clicking in this question, if you can give some tips I'll be very appreciate. It is best to show the complete code tutorial, because I am a newbie. Thanks a lot!

 

[thomsa]

go to Options - Setup - Public navigation

disable it

 

[RoguePanda]

I just want to hide my sub navigation bar, not disable it. I mean 'combine' the sub navigation and main navigation bar together. No matter which page i am in, just show me the main navigation bar. In other words, I want to make the main navigation bar always collapsible.