::selection {
  background: gold;
}
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";  
  line-height: 24px;
}

h1 {
  font-size: 1.5em;
}
h2 {
  font-size: 1.2em;
}

a {
  color: blue;
}
a:hover {
  background: yellow;
}

iframe {
  width: 100%;
}
img {
  max-width: 100%;
}

blockquote {
  border-left: 4px solid gold;
  margin: 0;
  padding-left: 1em;
}

nav.main {
  text-align: center;
}

main {
  max-width: 740px;
  margin: 2em auto;

  padding: 1em;
  padding-bottom: 2em;
  box-shadow: -0.4rem 0.4rem 2rem rgba(0,0,0,0.1);
  background: #fff;
  border-radius: 2px;
}

@media screen and (min-width: 500px) {
  main {
    padding: 1.5em;
  }
}

.call-to-action {
  display: inline-block;
  background: linear-gradient(to right, yellow, gold);
  border: 3px solid goldenrod;
  border-radius: 5px;
  padding: .5em 1em;
  font-weight: bold;
  text-decoration: none;
}


.callout {
  background: #ffffe5 linear-gradient(to right, #fffff5, #fffff9);
  padding: .5em;
  border-radius: 5px;
  border: 3px solid #d5d5d5;
  margin: 1em 0;
}
.checkpoint.callout {
  border-color: yellowgreen;
}
.callout:hover {
  background: #ffffe5 linear-gradient(to right, #ffffe5, #fffff9);
  border-color: gold;
}
.checkpoint.callout:hover {
  border-color: green;
}
.question.callout ol {
  list-style-type: upper-latin;
}
.callout::before {
  font-weight: bold;
}
.question.callout::before {
  content: 'Question';
}
.action.callout::before {
  content: 'Action';
}
.checkpoint.callout::before {
  content: '✅ Check Point';
  font-size: 1.5em;
}


details summary {
  cursor: pointer;
  color: #999;
}
details summary:hover {
  color: black;
}
.question.callout details em {
  color: green;
}