Display current Bootstrap v4 size on screen

_display-bootstrap-size.scss

/*
Inspired by https://www.viget.com/articles/check-your-breakpoint-using-this-simple-css-snippet
*/
body:after {

  color: #000;
  font-family: Helvetica;
  font-size: 12px;
  padding: 5px;
  font-weight: bold;
  right: 10px;
  position: fixed;
  text-align: center;
  text-transform: uppercase;
  bottom: 10px;
  width: 200px;
  z-index: 9999;
  background: #c0c0c0;
  border: solid 1px #000;
  
  @each $name, $value in $grid-breakpoints {
      @include media-breakpoint-up($name) {
        content: '#{$name} - min-width: #{$value}';
      }
  }

}

Nice one. Foundation has a similar approach using <meta>.

Injection of the tag:
https://github.com/zurb/foundation-sites/blob/5168d1f02ce8a95590f0e8f99d0d6c7a29b527e9/dist/js/plugins/foundation.core.js#L265-L267

Styling values as CSS content:
https://github.com/zurb/foundation-sites/blob/develop/scss/_global.scss#L115-L118

After finding your snippet and not finding what I was looking for, I just made it. here it is for those who are looking for a sample bootstrap way of finding bootstrap breakpoints : https://codepen.io/Unicornist/pen/WPWaBP