JSFiddle - React, Tailwind, and code Playground

HTML

<h1>H1 Content</h1>
<div class='clear'></div>
<p>More content here...</p>

CSS

h1 {
    /* Border added for visual effect */
    border: 1px solid #F00;
    clear: both;
    
    /* Remove the float: left to see that the H1 will extend to 100% width */
    float: left;
}

/* 
    Clear content after a floated element, more information can be found here:
    http://www.quirksmode.org/css/clearing.html
*/
.clear {
    clear: both;            
}