<h1 class="cp_h1title">見出しテキスト</h1>
.cp_h1title {
position: relative;
padding: .3em;
background: #00ACC1;
border-radius: 8px;
color: #ffffff;
}
.cp_h1title:after {
position: absolute;
content: '';
top: 100%;
left: 20px;
border: 10px solid transparent;
border-top: 10px solid #00ACC1;
width: 0;
height: 0;
}