背景色と角に三角矢印

HTML

<a href="">私たちについて</a>

CSS

a {
  display: block;
  position: relative;
  padding: 30px;
  width: 260px;
  color: #333;
  font-size: 18px;
  font-weight: 700;
  text-decoration: none;
  background-color: #90be70;
  border-radius: 40px 40px 0 40px;
}

a::before {
  content: '';
  position: absolute;
  bottom: 7px;
  right: 7px;
  width: 0;
  height: 0;
  border-style: solid;
  border-color: rgba(0 0 0 / 0) rgba(0 0 0 / 0) #2b550e rgba(0 0 0 / 0);
  border-width: 0 0 14px 14px;
}