to use <p class="wide">something</p>

fullwidth.css

//add <p class="wide"> to make a <p> stretch a grey background across full width
.wide {
  background-color: #aaa;
  position: relative;
  padding: 20px 0;
}

.wide:before,
.wide:after {
  content: ' ';
  background-color: #aaa;
  position: absolute;
  display: compact;
  width: 9999px;
  height: 100%;
}

.wide:before {
  left: -9999px;
  top: 0px;
}

.wide:after {
  top: 0px;
  right: -9999px;

}

//we need to stop the wide banners :before and :after making the page to wide - hide overflow
.l-page {
  width: 100%;
  overflow-x: hidden;
}

updated to very wide sideblobs just for @seutje ;-)