<div class="container">
  <div class="box"></div>
</div>

.container {
  width: 400px;
  height: 200px;
  overflow: auto;
}

.box {
  width: 100%;
  height: 400%;
  background: linear-gradient(#2e8b57 30px, #ffcc00 30px, #ffcc00 40px);
  background-size: 100% 50px;
}