div.sidebar {
  float: left;
  text-align: center;
}
div.main_div {
  margin-left: 150px;
  padding-top: 10px;
  min-height: 240px;
}
div.main_div::after {
  clear: both;
}
footer {
  text-align: center;
  font-size: 0.9em;
}

small {
  margin-left: 60px;
}

pre {
  background-color: black;
  color: lawngreen;
  padding: 10px;
  margin-left: 50px;
  overflow: auto;
  width: 90%;
}

div.note_tip {
  background-color: lightblue;
  margin-left: 50px;
  margin-right: 50px;
  padding: 10px;
}