CSS for the navigation menu

style.css

*,
*:before,
*:after {
  padding: 0;
  margin: 0;
  box-sizing: border-box;
}

:root {
  --darkbg: #222222;
  --darklight: #ffeaff;
  --red001: #ec0e0e;
}

html {
  height: 100vh;
}

body {
  font-size: 16px;
  font-family: Nunito, sans-serif;
}

.hamburger {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  position: absolute;
  cursor: pointer;
  display: flex;
  height: 50px;
  width: 50px;
  background: var(--darkbg);
  border: 1px solid transparent;
  top: 16px;
  right: 16px;
  z-index: 10;
  transition: border 0.3s ease;
}

.hamburger:active {
  outline: 5px solid var(--red001);
}

.hamburger::after,
.hamburger::before {
  content: '';
  height: 20px;
  border-left: 1px solid var(--darklight);
  transform: rotate(90deg);
  margin: -3px;
  transition: transform 0.3s ease;
}

.hamburger--active::after {
  transform: rotate(-135deg);
}
.hamburger--active::before {
  transform: rotate(-45deg);
}

.main__nav {
  display: flex;
  flex-direction: column;
  position: absolute;
  justify-content: center;
  align-items: center;
  height: 100vh;
  width: 100vw;
  background: var(--darkbg);
  transform: translateX(100%);
  transition: transform 0.5s ease;
}

.main__nav--active {
  transform: translateX(0);
}

.main__nav a {
  color: var(--darklight);
  font-size: 3rem;
  padding: 0.2em 0;
  margin: 0.6em;
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: border-bottom 1s ease;
}

.main__nav a:hover {
  border-bottom: 1px solid var(--darklight);
}

.main__nav a:focus, .main__nav a:active{
  border: 5px solid var(--red001)
}