title: Error: Undefined variable: "$alert-padding-y"
body: <p>I am using ruby 2.4.1 and rails 5.2.2, I want to add bootstrap 4 to my existing project. I removed all the css and js files from assets and just imported bootstrap in my application.scss and required in application.js file. But when page is opened it is giving error:</p>
  
  <p>ActionView::Template::Error (Error: Undefined variable: "$alert-padding-y".
          on line 7 of ../../.rvm/gems/ruby-2.4.1/gems/bootstrap-4.2.1/assets/stylesheets/bootstrap/_alert.scss</p>
  
  <blockquote>
    <blockquote>
      <p>padding: $alert-padding-y $alert-padding-x;</p>
    </blockquote>
  </blockquote>