atom/static/tree-view.css

.tree-view {
  height: 100%;
  background: black;
  color: white;
  overflow: auto;
  padding: 0 1em;
  cursor: default;
  font: 16px Inconsolata, Monaco, Courier !important;
}

.tree-view .disclosure-arrow {
  width: 2ex;
  display: inline-block;
}

.tree-view .directory .entries {
  padding-left: 1ex;
}

.file, .directory > .header {
  padding: 0 1ex;
}

.tree-view .directory .entries .file {
  padding-left: 3ex;
}

.tree-view .file.selected, .tree-view .directory.selected > .header {
  background: #444;
}

.tree-view:focus .file.selected, .tree-view:focus .directory.selected > .header {
  background: #a3fd97;
  color: black;
}