/* Put your CSS here */
html, body {
  margin: 20px;
  box-sizing: border-box;
}

h1, h2 {
  font-weight: normal;
}

#container {
  width: 300px;
  height: 200px;
  outline: 1px solid black;
  overflow: scroll;
  position: relative;
}

#scroller {
  position: absolute;
  background-color: blue;
  width: 100%;
}

.item {
  position: absolute;
  outline: 1px solid white;
  height: 40px;
  width: calc(100% - 10px);
  line-height: 40px;
  padding-left: 10px;
  color: white;
  background-color: green;
}