Scenario: 

You may have the scenario where you want to disable the toggle navigation button (image below) for specific web page. Ex: Contract agreement web page or Terms and Condition web page.  Where you dont want users to navigate to different links while reading T&C. 

In PowerApps Portal > Choose  any web page in responsive mode. You can see the below toggle navigation button.  This occurs because of the bootstrap theme. 

Solution:  In Terms and Condition Web page. 

In Portal management app:

1. Content > Web Pages > TermsAndCondition (Name of the web page) 

2. Under Localized Content > Select web page > Edit > Advanced 

Under Custom JavaScript section: Add the below JavaScript code to hide the toggle navigation bar element 

document.getElementsByClassName("navbar-toggle collapsed")[0].style.visibility = "hidden";

Hint: You can also apply jQuery as a replacement to hide your element. 

Hope this little trick is useful incase if you have the same scenario in your organization.