.sidenav {
  height: 100%;
  width: 0;
  position: fixed;
  z-index: 1;
  top: 0;
  left: 0;
  background-color: #111;
  overflow-x: hidden;
  transition: 0.5s;
  padding-top: 60px;
}

.sidenav a {
  padding: 8px 8px 8px 32px;
  text-decoration: none;
  font-size: 25px;
  color: #818181;
  display: block;
  transition: 0.3s;
}

.sidenav a:hover {
  color: #f1f1f1;
}

.sidenav .closebtn {
  position: absolute;
  top: 0;
  right: 25px;
  font-size: 36px;
  margin-left: 50px;
}

@media screen and (max-height: 450px) {
  .sidenav {padding-top: 15px;}
  .sidenav a {font-size: 18px;}
}

#####################################################

:root {
  --blue: #3498db;
  --dark-blue: #2980b9;
  --background: #081118;
  --grey: #333;
  --light-grey: #3b3b3b;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: sans-serif;
}

body {
  display: flex;
  align-items: left;
  justify-content: left;
  min-height: 100vh;
  background: var(--background);
}

.menu {
  width: 20rem;
  border-radius: 0.2rem;
  overflow: hidden;
}
.menu a {
  text-decoration: none;
}

.menu-item {
  list-style: none;
  border-top: 1px solid var(--dark-blue);
  overflow: hidden;
}

.btn {
  display: block;
  padding: 1rem 1.2rem;
  background: var(--blue);
  color: white;
  position: relative;
}
.btn::before {
  content: '';
  position: absolute;
  width: 1rem;
  height: 1rem;
  background: var(--blue);
  left: 1.5rem;
  bottom: -0.5rem;
  transform: rotate(45deg);
}
.btn i {
  margin-right: 1rem;
}

.menu-item__sub {
  background: var(--grey);
  overflow: hidden;
  transition: max-height 0.3s;
  max-height: 0;
}
.node-name {
  display: block;
  padding: 1rem 1.6rem;
  color: gray;
  font-size: 1.25rem;
}
.menu-item__sub a {
  display: block;
  padding: 1rem 1.6rem;
  color: white;
  font-size: 0.9rem;
  position: relative;
  border-bottom: 1px solid var(--light-grey);
}
.menu-item__sub a::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  width: 0.4rem;
  height: 100%;
  background: var(--blue);
  transform: translatex(-0.4rem);
  transition: 0.3s;
  opacity: 0;
}
.menu-item__sub a:hover::before {
  opacity: 1;
  transform: translatex(0);
}

.menu-item:target .menu-item__sub {
  max-height: 50em;
}