style.css

@import url("https://fonts.googleapis.com/css2?family=Roboto:ital,wght@0,100;0,300;0,400;0,500;0,700;0,900;1,100;1,300;1,400;1,500;1,700;1,900&display=swap");

:root {
  --color-x-light: hsl(19, 84%, 98%);
  --color-light: hsl(19, 84%, 88%); /* #fad6c5 */
  --color-light-sat: hsl(19, 24%, 58%);
  --color-dark: hsl(213, 44%, 15%); /* #152436 */
  --color-x-dark: hsl(213, 44%, 5%);

  height: 100%;
  margin: 0;
  color: var(--color-light);
  background-color: var(--color-dark);
  font-family: "Roboto", "Arial", sans-serif;
  font-weight: 400;
}

*,
*::before,
*::after {
  position: relative;
  box-sizing: border-box;
}

a {
  display: inline-block;
  color: var(--color-light);
  transition: all 250ms ease-in-out;
}
a:hover {
  color: var(--color-dark);
}

button {
  padding: 0.5em 1em;
  background-color: var(--color-light);
  border: 1px solid var(--color-dark);
  font-size: 1em;
  text-transform: uppercase;
  cursor: pointer;
}
button:hover,
button:has(+ #button-nav:popover-open),
button:where(:focus, :focus-visible, :focus-within) {
  background-color: var(--color-dark);
  color: var(--color-light);
}

button:where(:focus, :focus-visible, :focus-within),
label:has(+ input[type="checkbox"]:focus),
label:has(+ input[type="checkbox"]:focus-visible),
label:has(+ input[type="checkbox"]:focus-within) {
  outline: 2px dotted var(--color-dark);
  outline-offset: 2px;
}

header {
  position: -webkit-sticky;
  position: sticky;
  top: 0;
  z-index: 999;
  width: 100%;
  background-color: var(--color-light);
  padding: 0.5em 2em;
  display: flex;
  justify-content: flex-end;
  gap: 1em;
}
label {
  display: inline-block;
  background-color: var(--color-light);
  color: var(--color-dark);
  border: 1px solid var(--color-dark);
  padding: 0.5em 1em;
  text-transform: uppercase;
  cursor: pointer;
}
label:hover,
label:has(+ input[type="checkbox"]:focus),
label:has(+ input[type="checkbox"]:focus-visible),
label:has(+ input[type="checkbox"]:focus-within),
label:has(+ input[type="checkbox"]:checked) {
  background-color: var(--color-dark);
  color: var(--color-light);
}

input[type="checkbox"] {
  inset: 0;
  position: absolute;
  opacity: 0;
  pointer-events: none;
}
nav {
  & ul {
    margin: 0;
    padding: 0;
    list-style: none;
    display: flex;
    flex-direction: column;
    background-color: var(--color-light);
    color: var(--color-dark);
    & li {
      border: 1px solid var(--color-dark);
      & > * {
        padding: 0.5em 1em;
      }
    }
    & li + li {
      border-top: 0;
    }
    & li:hover {
      background-color: var(--color-light-sat);
      color: var(--color-light);
      & a {
        color: var(--color-x-light);
      }
    }
    & a {
      display: inline-block;
      color: var(--color-dark);
    transition: none;
    }
    & a:hover {
      color: var(--color-light);
    }
  }
}
#checkbox-nav {
  position: absolute;
  top: calc(53px - .5em);
  right: 0;
  overflow: hidden;
  & ul {
    opacity: 0;
    transform: translateY(-200%);
    transition: transform 250ms ease-in-out;
  }
}

input[type="checkbox"]:checked + #checkbox-nav > ul {
  opacity: 1;
  transform: translateY(0);
}

#button-nav {
  position: fixed;
  background: none;
  border: 0;
}

#button-nav:popover-open {
  display: flex;
  justify-content: flex-end;
  margin: 53px 0 auto auto;
  padding: 0 2em;
}