header {
  background-color: #ffffff;
  border-bottom: 1px solid #ff0000;
  display: flex;
  justify-content: space-between;
  padding: 0 1rem;
  transition: height 300ms;
  position: sticky;
  top: 0;
  left: 0;
  width: 100%;
  align-items: center;
  z-index: 2;
}

header.header-at-top .header-site-title {
  font-size: 2em;
}

.header-site-title {
  font-size: 1.25em;
  font-weight: 300;
  transition: font-size 300ms;
  padding: 0.5em 0;
}

.header-site-title a,
header nav a {
  text-decoration: none;
}

header nav {
  display: flex;
  font-size: 1em;
  column-gap: 15px;
  transition: font-size 300ms;
  padding-right: 0.5em;
}