<h1 class="cp_h1title">見出しテキスト</h1>

.cp_h1title {
  position: relative;
  background: #F8BBD0;
  box-shadow:0 1px 3px rgba(0,0,0,0.4);
}
.cp_h1title:before,
.cp_h1title:after {
  position: absolute;
  content: '';
  bottom: -15px;
  width: 15px;
  height: 15px;
  background: #EC407A;
}
.cp_h1title:before {
  right: 0;
  clip-path: polygon(0 0, 0% 100%, 100% 0);
}
.cp_h1title:after {
  left: 0;
  clip-path: polygon(100% 0, 0 0, 100% 100%);
}