body {
  margin: 0;
}
#app {
  display: grid;
  grid-template-columns: 250px 1fr;
  grid-template-rows: auto 1fr;
  height: 100vh;
}
#header {
  background-color: #446cb3;
  color: #fff;
  grid-column: 1 / 3;
  padding: 1rem;
}
#sidebar {
  background-color: #eee;
  overflow-y: auto;
  padding: 1rem;
}
#content {
  overflow: auto; /* seems to be part of the problem, together with the grid layout */
  padding: 0 1rem;
}
#test-subject {
  background-color: rgba(255, 0, 255, 0.7);
  bottom: 0;
  height: 50px;
  left: 0;
  width: 100%;
}