<h1 class="cp_h1title"><span class="main">見出しテキスト</span><span class="sub">サブテキスト</span></h1>

.cp_h1title {
  position: relative;
  line-height: 1;
  border-bottom: 1px solid #303f9f;
  padding-bottom: 10px;
}
.cp_h1title span.main {
  position: relative;
  color: #ffffff;
  background: #303f9f;
  padding: 5px 10px;
}
.cp_h1title span.main::after {
  position: absolute;
  content: '';
  top: 0;
  right: -10px;
  border-width: 10px 10px 0 0;
  border-style: solid;
  border-color: #303f9f transparent transparent transparent;
}
.cp_h1title span.sub {
  position: absolute;
  right: 0;
  bottom: 50%;
  color: #424242;
  font-size: 70%;
  width: 100%;
  text-align: right;
}