nav ul {
  display: flex;
}
nav ul li {
  margin: 5px 15px;
}
.tab-content {
  display: none;
  border: 1px solid #ccc;
  padding: 10px;
}
html:not(:has(:target)) .tab-content:first-of-type,
.tab-content:target,
.tab-content:has(:target),
.tab-content:target .tab-content:first-of-type {
  display: block;
}