图片很模糊，但应该是这样的。

*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding:0;
}

.button {
  display: flex;
  flex-flow: row nowrap;
  justify-content: space-around;
  align-items: center;
  border: none;
  border-radius: .5rem;
  overflow: hidden;
  color: white;
  font-size: 1.3rem;
}

.button > * {
  padding: .5rem .8rem;
}

.tick {
  background: green;
}
 
.content {
  background: lightblue;
}

<button type="button" class="button">
  <div class="tick">v</div>
  <div class="content">Start</div>
</button>