#container {
  background-color: #eee;
  width: 825px;
  height: 600px;
  margin: 0 auto;
  border: 1px solid black;
}

.focusable {
  outline: 0;
  cursor: default;
}

.focusable:focus {
  outline: 3px solid red;
}

.leftbox {
  float: left;
  height: 100%;
  background-color: gray;
  overflow-y: scroll;
  position: relative;
}

.rightbox {
  float: right;
  width: 580px;
  padding-right: 10px;
}

.leftbox .focusable {
  background-color: blue;
  width: 200px;
  height: 80px;
  margin: 10px 5px;
  color: white;
  text-align: center;
  line-height: 80px;
}

.leftbox .focusable.checked {
  background-color: purple;
}

.rightbox .content {
  display: none;
}

.rightbox .content.visible {
  display: block;
}

.rightbox .focusable {
  display: inline-block;
  background-color: green;
  width: 200px;
  height: 30px;
  margin: 10px 5px;
  color: white;
  text-align: center;
  line-height: 30px;
}

#sidebox {
  width: 825px;
  margin: 1em auto 0 auto;
}