menuStyle.css

body {
  margin: 0;
  display: flex;
  min-height: 100vh;
}

nav {
  width: 250px;
  transition: margin-left 300ms;
  position: relative;
  z-index: 98;
}

article {
  transition: left 600ms;
}

ul.sidenav {
  background-color: var(--light);
  list-style-type: none;
  padding: 0;
  top: 0;
  height: 100vh;
  margin-top: 0;
  margin-bottom: 0;
  overflow-x: hidden;
  overflow-y: auto;
  position: -webkit-sticky;
  position: -moz-sticky;
  position: -o-sticky;
  position: -ms-sticky;
  position: sticky;
  box-shadow: inset -5px 0px 25px -10px var(--dark);
  font-family: "Trebuchet MS", "Lucida Sans Unicode", "Lucida Grande",
    "Lucida Sans", Arial, sans-serif;
}

ul.sidenav::-webkit-scrollbar {
  display: none;
}

ul.sidenav > li:first-child {
  padding-top: 1em;
}

ul.sidenav > li:last-child {
  padding-bottom: 1em;
}

ul.sidenav li a:not(.title) {
  display: block;
  color: var(--main);
  padding: 8px 16px;
  text-decoration: none;
}

ul.sidenav li a.active {
  border-left: 4px solid var(--main);
  color: var(--dark);
  cursor: pointer;
}

ul.sidenav li a.title {
  display: block;
  color: var(--main);
  text-decoration: none;
  cursor: pointer;
}

ul.sidenav li ul {
  box-shadow: inset -5px 0px 25px -10px var(--dark);
  padding-left: 1em;
  background-color: var(--dimmed);
}

ul.sidenav li ul li a.active {
  border-left: 0px solid var(--main);
  text-decoration: underline;
}

ul.sidenav li a:hover:not(.active):not(.title) {
  background-color: var(--light-main);
  color: var(--light);
}

div.menuButton {
    width: 1em;
    height: 1em;
    margin-left: -17px;
    margin-right: 16px;
    padding: 8px;
    top: calc(50% - 16px);
    position: fixed;
    cursor: pointer;
    z-index: 99;
    background-color: var(--light-main);
    border-radius: 32px;
    transition: left 300ms;
    border: solid 2px var(--main);
}

div.menuButton > i {
    transform: translateX(3px) rotate(135deg);
    border: solid var(--dark);
    border-width: 0 3px 3px 0;
    display: inline-block;
    padding: 3px;
    width: 0.25em;
    height: 0.25em;
    transition: all 300ms;
}

@media screen and (max-width: 600px) {
    nav {
        position: fixed;
    }
}