tl-dr/style.css

@font-face {
  font-family: "DuctusRegular";
  font-weight: normal;
  src: local("DuctusRegular"), url("fonts/Ductus/DuctusRegular.otf") format("opentype"), url("fonts/Ductus/DuctusRegular.woff") format("woff");
}

@font-face {
  font-family: "CascadiaCode VTT";
  font-weight: normal;
  src: local("CascadiaCode VTT"), url("fonts/Cascadia/otf/CascadiaCode-Light.otf") format("opentype"), url("fonts/Cascadia/woff2/CascadiaCode-Light.woff2") format("woff2");
}

@font-face {
  font-family: "CascadiaCode VTT";
  font-weight: bold;
  src: local("CascadiaCode VTT"), url("fonts/Cascadia/otf/CascadiaCode-Bold.otf") format("opentype"), url("fonts/Cascadia/woff2/CascadiaCode-Bold.woff2") format("woff2");
}

/* 
TODO:
- fallback fonts
*/

:root {
  --background: #d1d1d1;
  --slider-height: 1.5rem;
  --text-color: black;
  --text-color-lighter: grey;
  --text-color-light: white;
}

body,
html {
  width: 100%;
  height: 100%;
}

body {
  margin: 0 0;
  padding: 0 0;
  font-family: "DuctusRegular", sans-serif;
  background-color: var(--background);
  display: grid;
  grid-template-columns: min-content 1fr min-content;
  grid-template-rows: min-content 50px 1fr 50px;
  grid-gap: 1rem 2rem;
  grid-template-areas:
    "header header header"
    ". s-top s-top"
    "s-left main aside"
    "s-left footer footer";
  max-width: 1200px;
  width: calc(100% - 4rem);
  margin: auto;
  height: calc(100svh - 4rem);
  margin: 2rem;
}

h1,
h2,
h3,
h4 {
  font-weight: normal;
  margin: 0 0;
}

h1 {
  font-size: 3rem;
}

main {
  grid-area: main;
  overflow: hidden;
  position: relative;
}

.main__inner {
  overflow: auto;
  height: 100%;
}

.main__background,
.main__background--radius {
  position: absolute;
  background-color: rgb(97, 97, 97);
  width: 100%;
  height: 100%;
  z-index: -1;
}

.main__background--radius {
  background-color: black;
  border-bottom-right-radius: 60%;
}

article h1,
article h2,
article h3 {
  margin-top: 1rem;
  margin-bottom: 0.5rem;
}

header {
  grid-area: header;
}

nav {
  display: flex;
  justify-content: center;
  align-items: center;
  position: relative;
}

.slider--top {
  grid-area: s-top;
}

.slider--left {
  grid-area: s-left;
}

article {
  max-width: 700px;
  width: calc(100% - 2rem);
  margin: 2rem auto;
  overflow-x: hidden;
  color: var(--text-color-light);
  display: flex;
  flex-direction: column;
  font-family: "CascadiaCode VTT";
}

article p,
article pre {
  margin: 0 0;
  font-size: 14px;
  line-height: 1.5;
}

article pre {
  color: green;
}

footer {
  grid-area: footer;
}

aside {
  grid-area: aside;
  writing-mode: vertical-rl;
  text-orientation: mixed;
}

nav label {
  position: absolute;
  right: 1rem;
  top: 50%;
  transform: translate3d(0, -50%, 0);
  color: var(--text-color-lighter);
  pointer-events: none;
}

.annotation {
  background-color: white;
  color: black;
  width: auto;
  max-height: 0px;
  overflow: hidden;
  display: inline-block;
  clear: both;
  transition: 1s linear max-height;
  font-family: "DuctusRegular";
  padding: 0px 2px;
  font-weight: lighter;
}

.annotation.visible {
  max-height: 99px;
}

.slider--left label {
  writing-mode: vertical-rl;
  top: 100%;
  transform: translate3d(100%, -120%, 0);
  right: 90%;
}

h3 {
  color: var(--text-color-lighter);
}

hr {
    width: 100%;
    margin: 2rem auto;
}
input[type="range"] {
  -webkit-appearance: none;
  appearance: none;
  width: 100%;
  cursor: pointer;
  outline: none;
  overflow: hidden;
  border-radius: 1rem;
  border: 1px solid black;
  transition: 0.2s linear;
}

input[type="range"]::-webkit-slider-runnable-track {
  height: var(--slider-height);
  background: var(--background);
  border-radius: 1rem;
  transition: 0.2s linear;
}

input[type="range"]::-moz-range-track {
  height: var(--slider-height);
  background: var(--background);
  border-radius: 1rem;
}

input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  height: calc(100% + 4px);
  margin-top: -2px;
  width: 150px;
  border-radius: 1rem;
  background-color: white;
  border: 1px solid black;
}

input[type="range"]::-moz-range-thumb {
  -webkit-appearance: none;
  appearance: none;
  height: calc(100% + 4px);
  margin-top: -2px;
  width: 150px;
  border-radius: 30px;
  background-color: white;
  border: 1px solid black;
}

input[type="range"].vertical {
  writing-mode: vertical-lr;
  height: 100%;
  width: var(--slider-height);
}

input[type="range"].vertical::-webkit-slider-runnable-track {
  width: var(--slider-height);
  height: 100%;
}

input[type="range"].vertical::-moz-range-track {
  width: var(--slider-height);
  height: 100%;
}

input[type="range"].vertical::-webkit-slider-thumb {
  height: 150px;
  width: var(--slider-height);
}

input[type="range"].vertical::-moz-range-thumb {
  height: 150px;
  width: var(--slider-height);
}