<h1 class="cp_h1title">見出しテキスト</h1>
.cp_h1title {
position: relative;
padding: .3em .3em .3em 1.3em;
}
.cp_h1title::after {
position: absolute;
content: '';
bottom: .8em;
left: .4em;
width: 12px;
height: 12px;
background-color: #da3c3c;
transform: rotate(45deg);
}