How to remove navbar rounded corners using border-radius property when using SASS for Ruby on Rails?

I will instead of modifying the css add the class: navbar-static-top

ie:

<nav class="navbar navbar-default navbar-static-top" role="navigation">

or the class navbar-fixed-top, if you want the menu to be fixed on the top(on large pages)

ie:

<nav class="navbar navbar-default navbar-fixed-top" role="navigation">