<p class="msr_btn03">
  <a href="#">button01</a>
</p>

.msr_btn03 {
  border-radius: 3px;
  box-sizing: border-box;
  width: 230px;
}
.msr_btn03 a {
  background-color: #1B73BA;
  border-radius: 3px;
  color: #FFFFFF;
  font-size: 13px;
  display: block;
  padding: 13px 10px;
  position: relative;
  text-align: center;
  text-decoration: none;
  transition: 0.2s ease-in-out;
  -o-transition: 0.2s ease-in-out;
  -moz-transition: 0.2s ease-in-out;
  -webkit-transition: 0.2s ease-in-out;
}

/* 白の三角形 */
.msr_btn03 a:before {
  border: 4px solid transparent;
  border-left: 4px solid #FFFFFF;
  box-sizing: border-box;
  content: "";
  display: inline-block;
  height: 8px;
  margin:0 4px 0 0;
  transition: 0.2s ease-in-out;
  -o-transition: 0.2s ease-in-out;
  -moz-transition: 0.2s ease-in-out;
  -webkit-transition: 0.2s ease-in-out;
  width: 4px;
  vertical-align:0px;
}

/* マウスオーバー */
.msr_btn03 a:hover {
  background-color: #F0F0F0;
  color: #1B73BA;
}
.msr_btn03 a:hover:before {
  border-left: 4px solid #1B73BA;
}