<div class="container">
  <div class="row">
    <div class="col small-12">
      <div class="grid-bg center">
        <strong>The Header</strong> (span the entire 12 columns on all screen size)
      </div>
    </div>
    <div class="col small-12 med-8">
      <div class="grid-bg"><strong>Content</strong> (span the entire 12 columns on small screen devices only and 8 columns for medium to large screen)<br /><br />
        Pellentesque habitant morbi tristique senectus et netus et.
      </div>
    </div>
    <div class="col small-12 med-4">
      <div class="grid-bg"><strong>Sidebar</strong> (span the entire 12 columns on small screen devices only and 4 columns for medium to large screen)</div>
    </div>
    <div class="col small-12">
      <div class="grid-bg center"><strong>The Footer</strong></div>
    </div>
  </div>
</div>

$num-cols: 12;
$spacing-width: 8px;

// mixins for generating percentage based columns
@mixin columns-generator($class-name) {
  $i: 1;
  @while $i <= $num-cols {
    $perc: unquote((100 / ($num-cols / $i)) + "%");
    
    .#{$class-name}#{$i} {
      width: $perc;
    }
    
    $i: $i + 1;
  }
}

// mixin for generating grid column
@mixin grid-columns-generator($class-name) {
  $i: 1;
  @while $i <= $num-cols {
    .#{$class-name}#{$i} {
      grid-column: span $i;
    }

    $i: $i + 1;
  }
}

body {
  background: #eee;
}

.container {
  max-width: 1280px;
  margin: 20px auto;
  padding: 0 8px;
}

.row {
  margin-left: -($spacing-width);
  margin-right: -($spacing-width);
  
  &:after {
    content: "";
    display: table;
    clear: both;
  }

  .col {
    box-sizing: border-box;
    float: left;
    padding: 0 $spacing-width;
  }
}

@include columns-generator("small-");

@media (min-width: 53em) {
  @include columns-generator("med-");
}

@media (min-width: 75em) {
  @include columns-generator("large-");
}

.center {
  text-align: center;
}

strong {
  font-weight: 600;
}

.grid-bg {
  background-color: #D24663;
  color: #FFFFFF;
  padding: 16px;
  margin: 0 0 1rem 0;
  font-weight: 200;
  font-size: 24px;
  line-height: 1.5;
}

// For browsers that supports grid, reset all the values above
@supports(display: grid) {
  .row {
    margin-left: auto;
    margin-right: auto;
    display: grid;
    grid-template-columns: repeat(12, 1fr);
    grid-gap: $spacing-width * 2;

    &:after {
      content: none;
    }
  }
  
  .grid-bg {
    margin: auto;
  }

  .row > * {
    width: auto;
  }

  .row .col {
    width: auto;
    padding: 0;
  }

  @include grid-columns-generator("small-");

  @media (min-width: 53em) {
    @include grid-columns-generator("med-");
  }

  @media (min-width: 75em) {
    @include grid-columns-generator("large-");
  }
}