styles.css

body {
  margin: 0;
  font-family: helvetica, sans-serif;
  font-size: 14px;
  line-height: 1.4;
}

#toolbar {
  display: flex;
  justify-content: space-between;
  position: fixed;
  width: 100%;
  top: 0;
  left: 0;
  padding: 8px;
  background-color: #222;
  color: #FFF;
}

#toolbar > div:last-child {
  margin-right: 18px;
}

main {
  padding-top: 30px;
  display: flex;
  justify-content: flex-start;
  align-items: stretch;
}

#tree {
  flex-basis: 20%;
  flex-grow: 1;
  padding: 8px;
  background-color: #EEE;
}

#tree nav {
  padding-left: 4px;
  font-size: 1.4rem;
  width: 1.0rem;
}

/* Default wedge is empty & closed */
#tree li > header nav {
  color: #888;
}

#tree li.with-kids > header nav {
  color: black;
}

#tree li > header .fa-angle-down {
  display: none;
}

#tree li.open > header .fa-angle-down {
    display: inline;
}

#tree li.open > header .fa-angle-right {
    display: none;
}

#tree li > ul {
    display: none;
}

#tree li.open > ul {
    display: block;
    /*border-left: solid 1px #FFF;*/
}

#tree h2 {
  margin: 4px;
  font-weight: normal;
  font-size: 1.0rem;
  white-space: nowrap;
}

#tree ul {
  list-style-type: none;
  margin-left: 10px;
  margin-bottom: 4px;
  padding-left: 0;
}

#tree li header {
  margin-left: 0;
  /*border-top: solid 1px #FFF;*/
  display: flex;
  justify-content: flex-start;
  cursor: pointer;
}

#tree li.current > header h2 {
  font-weight: bold;
}

#tree li:last-child {
  /*border-bottom: solid 1px #FFF;*/
}

#breadcrumbs {
    padding: 8px;
}

#editor {
  flex-basis: 80%;
  flex-grow: 2;

  display: flex;
  min-height: 100%;
  flex-direction: column;
}

#editor h1 {
  padding-left: 8px;
  font-size: 1.4rem;
}

#editor article {
  flex: 1;
  padding: 8px;
  font-size: 1.0rem;
}

#footer {
  padding: 8px;
  background-color: #EEE;
}