section:not(.active) {
  display: none;
  height: 0;
  overflow: hidden;
}

body {
  margin: 0;
}

header {
  text-align: center;
}

header::after {
  content: url(images/curve.svg);
}

section.active {
 margin: 10px;
}

#textpane {
  font-family: sans-serif;
}

summary {
  color: red;
}

details:not([open]) {
  display: inline;
}

details[open] {
  background-color: lightgray;
}

.a {
  min-width: 160px;
  display: inline-block;
}

.b {
  margin-left: 160px;
  margin-top: -1.2em;
  display: block;
}

nav a {
  text-decoration: none;
  font-weight: bold;
  font-size: 14pt;
  color: white;
}

nav a:hover {
  text-decoration: underline;
}

nav {
  background-color: black;
  background-image: url('images/bg.jpg');
  padding: 10px;
  color: white;
  text-shadow: 0 0 4px red;
  position: sticky;
  top: 0;
}

h1 {
  margin-top: 0;
  font-size: xx-large;
}

h3 {
  margin-top: 2em;
}

a[name] {
  line-height: 3em;
}