<h1 class="cp_h1title">見出しテキスト</h1>

.cp_h1title {
  position: relative;
  border: 1px solid #ec407a;
  padding: 5px 10px;
}
.cp_h1title::before,
.cp_h1title::after {/*カギ括弧のサイズ*/
  position: absolute;
  content: '';
  width: 10px;
  height: 20px;
  border: solid #ec407a;
  border-width: 1px 0 0 1px;
}
.cp_h1title::before {/*左のカギ括弧の位置*/
  top: 3px;
  left: 3px;
}
.cp_h1title::after {/*右のカギ括弧の位置*/
  bottom: 3px;
  right: 3px;
  transform: rotate(180deg);/*180度回転*/
}