.container {
  position: relative;
  overflow: hidden;
  width: 100%;
  padding-top: 56.25%;
}

.container > iframe {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

.center {
  text-align: center;
}

.justify {
  text-align: justify;
}

.text-center {
  text-align: center;
}

.text-justify {
  text-align: justify;
}

pre {
  border-radius: 8px;
  margin: 1em 0;
}

.callout-tip {
  background-color: #d4edda;
  border-left: 4px solid #28a745;
  padding: 15px;
  margin: 1em 0;
  border-radius: 4px;
}

.callout-note {
  background-color: #cce5ff;
  border-left: 4px solid #004085;
  padding: 15px;
  margin: 1em 0;
  border-radius: 4px;
}

.callout-warning {
  background-color: #fff3cd;
  border-left: 4px solid #856404;
  padding: 15px;
  margin: 1em 0;
  border-radius: 4px;
}