<div class="cp_card">
コンテンツ
  <div class="cp_ribbon11">
    <div class="cp_ribbon">Ribbon</div>
  </div>
</div>

.cp_card {
  position: relative;/*リボンをかけたいコンテンツボックスにセット*/
  width: 300px;
  height: 300px;
  background: #ffffff;
  margin: auto;
  padding: 60px 5px 0;
  box-shadow: 0 0 5px rgba(0, 0, 0, 0.3);
}
/*リボンの設定*/
.cp_ribbon11 {
  line-height: 50px;
  position: absolute;
  top: 15px;
  display: flex;
  justify-content: center;
  align-items: center;
  width: calc(100% + 10px);
  height: 40px;
  margin-right: -10px;
  margin-left: -10px;
  text-align: center;
  color: #ffffff;
  background: #2196F3;
}
/*リボンの影の共通設定*/
.cp_ribbon11:before,
.cp_ribbon11:after {
  position: absolute;
  top: 100%;
  content: '';
  border-top: 5px solid #1565C0;
  border-left: 5px solid transparent;
}
.cp_ribbon11:before {
  left: 0;
}
.cp_ribbon11:after {
  right: 0;
  transform: scale(-1, 1);/*左右反転*/
}