SOURCE

<div class="sew">
  这是一则贴士(缝边风格)
</div>

<div class="mask">
  这是一则贴士(渐变风格)
</div>

.sew{
  width:300px;
  height:200px;
  margin:100px 100px;
  background:	#008B8B ;
  border:white dashed 5px;
  outline:	#008B8B solid 20px;
  border-radius:40px;
/*   outline-offset:-5px; */
  box-shadow:0 0 0 18px #008B8B;
  box-sizing:border-box;
  padding:20px;
}

.mask{
  width:300px;
  height:200px;
  margin:100px 100px;
  background:	#008B8B;
  box-sizing:border-box;
  padding:20px;
  border-radius:10%;
  background-image:
    linear-gradient(45deg,transparent 25%,rgba(255,255,255,0.2) 0,rgba(255,255,255,0.2),75%,transparent 0);
}