body {
  font-family: system-ui, sans-serif;
  max-width: 60ch;
  padding: 2ch;
  margin: auto;
  color: #222;
  background: #e1edf5;
}
h1, h2, h3 {
  font-family: ui-serif, Times, serif;
}
a{color:#a44}
a:visited{color:#555}
img{max-width:100%}
pre{overflow:auto}
table,th,td{border:1px solid;padding:.5rem;border-collapse: collapse}

nav ul{display: none; list-style: none; padding: 0}
nav #checkbox{opacity: 0}
nav #checkbox:checked + ul{display: block