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HTML

              
                # Breakpoint Helper
<section>
<-- Resize your browser -->
  
  Breakpoint helper works by taking a SCSS map with information about your breakpoints, and mapping them to an aside to help front-end developers visualize which breakpoint they are actively on without needing to open the console.
</section>
              
            
!

CSS

              
                @charset "UTF-8";

// We use a scss map to iterate over the selectors, as well as generating the media query
$bp-helper-map: (
    ( short-label: 'xs', 
      full-label: '$media-xs', 
      media: 'only screen and (max-width: 575px)', 
      color: #0074D9)
    ,(short-label: 'sm', 
      full-label: '$media-sm', 
      media: 'only screen and (min-width: 576px) and (max-width: 767px)',
      color: #3D9970 )
    ,(short-label: 'md', 
      full-label: '$media-md', 
      media: 'only screen and (min-width: 768px) and (max-width: 991px)', 
      color: #FF851B )
    ,(short-label: 'lg', 
      full-label: '$media-lg', 
      media: 'only screen and (min-width: 992px) and (max-width: 1199px)', 
      color: #FF4136 )
    ,(short-label: 'xl', 
      full-label: '$media-xl', 
      media: 'only screen and (min-width: 1200px)', 
      color: #B10DC9)
); // map

@mixin breakpoint-helper($selector: '#breakpoint-helper', $map: $bp-helper-map ) {
  // Most of this is default styling so the element is fixed top-right
  #{$selector} {
    background-color: transparentize(grey, .2);
    border-radius: 3px;
    border-top-right-radius: 0;
    border-bottom-right-radius: 0;
    box-shadow: $material-shadow;
    color: white;
    display: block;
    font-size: .75em;
    line-height: 1;
    padding: .5em;
    position: fixed;
    right: -3.5em;
    top: 1rem;
    transition: all .25s ease-in;
    width: 6em;
    white-space: nowrap;
    z-index: 9999;

    &:hover, &:active, &:focus {
      box-shadow: $material-shadow--hover;
      transition: all .25s ease-out;
      right: 0;
      overflow: hidden;
      font-size: 1em;
    }

    // Iterate over the map and output all the breakpoints
    @each $_map in $map {
      $_short-label: map-get($_map, short-label);
      $_full-label: map-get($_map, full-label);
      $_media: map-get($_map, media);
      $_color: map-get($_map, color);

      @media #{$_media} {
        background-color: $_color;

        &:after {
          content: "#{$_short-label}";
        }

        &:hover, &:active, &:focus {
          &:after {
            content: "#{$_full-label}";
          }
        }
      }
    }
  }
}

@include breakpoint-helper();
              
            
!

JS

              
                // Original jQuery Refactored as ES6

// Check if we are in a predetermined development environment
if ((window.location.hostname.indexOf("localhost") > -1) || (window.location.hostname.indexOf("dev") > -1) || (window.location.hostname.indexOf("codepen") > -1)) {

// Finds the first script inside the body
const bodyElement = document.querySelector('body > script:first-of-type');

// Insert breakpoint helper before the script.
bodyElement.insertAdjacentHTML('beforebegin', `<aside id="breakpoint-helper" tabindex="-1" aria-hidden="true"></aside>`);
}
              
            
!
999px

Console