.sandbox {
  border: 1px solid #ccc;

  margin: 0.5em 0;
  padding: 1em;
}
.sandbox button {
  font-size: 11pt;

  margin: 4px;
}
.sandbox .boxes {
  background: #333333;
  border: 2px inset #d0d0d0;
  border-radius: 5px;

  box-sizing: border-box;
  display: block;
  padding: 4px;
  width: 100%;
  min-height: 100px;
}
.sandbox .box {
  background: #5c5c5c;
  border: 1px outset #f0f0f0;
  border-radius: 5px;
  color: #eeeeee;

  vertical-align: middle;

  box-sizing: border-box;
  display: inline-block;
  margin: 2px;
  padding: 2px;
  width: 80px;
  height: 80px;
}
.sandbox b { font-weight: bold; }
.sandbox i { font-style: italic; }

code {
  counter-reset: code-lines;

  box-sizing: border-box;
  display: block;
  position: relative;
  margin: .8em 0;
  padding: 4px 8px 8px;

  font-family: Monaco, Courier, monospace;
  font-size: 10pt;
}
code:before {
  border-bottom: 1px dotted #888888;
  color: #555555;

  content: 'code';
  font-size: 80%;

  display: block;
  margin: 0 0 .8em;
  padding: 1px 4px;
}
code.html:before { content: 'html'; }
code.js:before { content: 'javascript';
}
code .line {
  counter-increment: code-lines;

  display: block;
  position: relative;
  padding-left: 44px;
}
code .line:hover {
  background: #e8e8e8;
}
code .line.comment {
  color: #886e55;
}
code .line:before {
  user-select: none;
  -webkit-user-select: none;

  border-right: 1px solid #888888;
  color: #555555;
  content: counter(code-lines);
  font-size: 90%;
  text-align: right;

  box-sizing: border-box;
  display: inline-block;
  position: absolute;
  padding: 2px;
  width: 40px;
  height: 100%;
  left: 0;
}