JSFiddle - React, Tailwind, and code Playground

HTML

<div id="wrapper" class="cf">
    <div>Hello World</div>
    <div>Hello World</div>
</div>

CSS

#wrapper{
    border:1px solid red;
}

#wrapper div{
    float:left;
    font-size: 3em;
}
/* For modern browsers */
.cf:before,
.cf:after {
    content:"";
    display:table;
}

.cf:after {
    clear:both;
}

/* For IE 6/7 (trigger hasLayout) */
.cf {
    zoom:1;
}