Issue description

Navbar with .fixed-top className overshadows Modal. Modal has the default zIndex set to 1000 while Navbar.fixed-top has zIndex set to 1030. The problem can be fixed by setting Modal zIndex property to greater than 1030.

• version #4.2.0
• components: Modal

Steps to reproduce issue

http://codepen.io/alihammad-gist/pen/MpwBeY

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