#tab-bar {
  display: flex;
  background: #ddd;
  padding: 4px;
}
#tab-bar button {
  margin-right: 4px;
  padding: 6px 10px;
  border: none;
  background: #eee;
}
#tab-bar button.active {
  background: white;
  border-bottom: 2px solid dodgerblue;
}