aside {
  width: 200px;
  position: fixed;
  top: 0;
  bottom: 0;
  padding: 8px;
  display: flex;
  align-items: stretch;
}

aside .tree-view {
  width: 100%;
  overflow-y: scroll;
}

main {
  width: 65rem;
  margin-left: 240px;
  margin-bottom: 60px;
}