<div class="caption_box"> <h1 class="caption">caption</h1> <p>Hello World!, content.....</p> </div> .caption_box{ position: relative; margin-top: 1em; padding: 1em 2em; border: 1px solid black; } .caption_box .caption{ position: absolute; top: 0; left: 0; font-size: 1em; padding: 0 1em; margin: 0; background-color: white; transform: translateY(-50%) translateX(1em); } 解説 親要素にborderとposition: relat