:root {
  --space: 1rem;
  --border: 4px;
  --page-width: 80ch;
  --font-family: 'Helvetica', sans-serif;
  --color-link: black;
  --color-active: royalblue;
  --ease: cubic-bezier(0.23, 1, 0.32, 1);
  --duration: 350ms;
  --section-offset: 0;
}

* {
  box-sizing: border-box;
}

html {
  --scroll-behavior: smooth;
  scroll-behavior: var(--scroll-behavior);
}
@media (prefers-reduced-motion: reduce) {
  html {
    --scroll-behavior: auto;
  }
}

body {
  font-family: var(--font-family);
  line-height: 1.5;
}

h1, h2, h3 {
  font-weight: bold;
  line-height: 1.25;
}

h1 {
  font-size: 2.75rem;
}

h2 {
  font-size: 2.25rem;
}

h3 {
  font-size: 1.5rem;
}

ul:not(.menu) {
  list-style-type: disc;
  margin-left: var(--space);
}
ul:not(.menu) > li + li {
  margin-top: var(--space);
}

.nav-sections {
  position: -webkit-sticky;
  position: sticky;
  top: 0;
  width: 100%;
  background-color: white;
  box-shadow: inset lightgray 0 -1px 0, rgba(0, 0, 0, 0.15) 0 3px 10px 0;
  z-index: 100;
}
.nav-sections .menu {
  position: relative;
  display: flex;
  flex-wrap: nowrap;
  overflow: scroll;
  -ms-scroll-chaining: none;
      overscroll-behavior: none;
  scrollbar-width: none;
  -ms-overflow-style: none;
  margin: 0 auto;
  max-width: var(--page-width);
  -webkit-transform: translateZ(0);
          transform: translateZ(0);
  transition: -webkit-transform var(--ease) var(--duration);
  transition: transform var(--ease) var(--duration);
  transition: transform var(--ease) var(--duration), -webkit-transform var(--ease) var(--duration);
}
.nav-sections .menu::-webkit-scrollbar {
  display: none;
}
.nav-sections .menu-item-link {
  display: block;
  padding: calc(var(--space) * 1.5) var(--space);
  text-decoration: none;
  white-space: nowrap;
  color: var(--color-link);
  transition: color var(--ease) var(--duration);
}
.nav-sections .menu-item-link.active {
  color: var(--color-active);
}

.active-line {
  position: absolute;
  bottom: 0;
  left: 0;
  height: 4px;
  background-color: var(--color-active);
  transition: width var(--ease) var(--duration), -webkit-transform var(--ease) var(--duration);
  transition: width var(--ease) var(--duration), transform var(--ease) var(--duration);
  transition: width var(--ease) var(--duration), transform var(--ease) var(--duration), -webkit-transform var(--ease) var(--duration);
}

.placeholder-section {
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  height: 50vh;
  background-color: lightgray;
}

.page-sections {
  margin: 0 auto;
  max-width: var(--page-width);
}

.page-section {
  margin: calc(var(--space) * 2) 0;
  padding: calc(var(--space) * 2) var(--space);
}
.page-section > * + * {
  margin-top: calc(var(--space) * 1.5);
}

.section-title {
  outline: none;
}
.section-title:before {
  content: "";
  display: block;
  visibility: hidden;
  pointer-events: none;
  margin-top: calc(var(--section-offset) * -1px);
  height: calc(var(--section-offset) * 1px);
}