@keyframes expand {
  0% {
    opacity: 0;
    max-height: 0;
  }
  100% {
    opacity: 1;
    max-height: 30em;
  }
}
html {
  overflow-y: scroll;
}

body {
  position: relative;
  background: #f0f4f9;
  line-height: 1.6;
  font-family: -apple-system, BlinkMacSystemFont, Segoe UI, Roboto, Helvetica, Arial, sans-serif;
}

main {
  display: block;
  /* IE */
  width: 70%;
  max-width: 50em;
  margin: 3em auto;
}

p {
  margin: 0;
}

p + p {
  margin-top: 1.5em;
}

a {
  color: #1e90ff;
}

details > div {
  position: relative;
  z-index: 20;
  padding: 1.25em 1.5em;
  margin-bottom: .6em;
  border-radius: 0.3em;
  box-shadow: 0 15px 35px rgba(50, 50, 93, 0.1), 0 5px 15px rgba(0, 0, 0, 0.07);
  background-color: white;
}

summary {
  position: relative;
  z-index: 10;
  display: block;
  background: white;
  padding-left: 3em;
  margin-bottom: .5em;
  font-size: 1.2em;
  line-height: 3;
  box-sizing: border-box;
  list-style: none;
  cursor: pointer;
  border-radius: 0.3em;
  box-shadow: 0 15px 35px rgba(50, 50, 93, 0.1), 0 5px 15px rgba(0, 0, 0, 0.07);
}

summary:hover,
summary:focus {
  background: #1e90ff;
  color: white;
  text-shadow: 0 -1px 0 rgba(0, 0, 0, 0.5);
  outline: 0;
}

summary::-webkit-details-marker {
  display: none;
}

summary::before {
  content: '+';
  position: absolute;
  top: 50%;
  left: 1em;
  transform: translateY(-50%);
  width: 1em;
  height: 1em;
  margin-right: 1em;
  background: #ff5321;
  color: white;
  font-family: Arial, sans-serif;
  font-size: 20px;
  line-height: 1;
  text-align: center;
  border-radius: 50%;
}

details[open] summary::before {
  content: '-';
  line-height: .9;
}

details[open] summary:hover::before,
details[open] summary:focus::before {
  background: white;
  color: #1e90ff;
}