style.css

.tab-button {
  padding: 6px 10px;
  border-top-left-radius: 3px;
  border-top-right-radius: 3px;
  border: 1px solid #ccc;
  cursor: pointer;
  background: #f0f0f0;
  margin-bottom: -1px;
  margin-right: -1px;
}
.tab-button:hover {
  background: #e0e0e0;
}
.tab-button.active {
  background: #e0e0e0;
}
.tab {
  border: 1px solid #ccc;
  padding: 10px;
}
.posts-tab {
  display: flex;
}
.posts-sidebar {
  max-width: 40vw;
  margin: 0;
  padding: 0 10px 0 0;
  list-style-type: none;
  border-right: 1px solid #ccc;
}
.posts-sidebar li {
  white-space: nowrap;
  text-overflow: ellipsis;
  overflow: hidden;
  cursor: pointer;
}
.posts-sidebar li:hover {
  background: #eee;
}
.posts-sidebar li.selected {
  background: lightblue;
}
.selected-post-container {
  padding-left: 10px;
}
.selected-post > :first-child {
  margin-top: 0;
  padding-top: 0;
}