gistfile1.txt

:root {
  --sizeBody: 16px;  /* 1rem = 16px */
  --navHeight: 4rem; /* 4 * 16px = 64px */
}

.nav {
  height: var(--navHeight); 
} 

@media (min-width: 1000px) {
  :root {
    --sizeBody: 20px;
  }

  /*
    --navHeight is still
    4 * 16px = 64px
    and NOT
    4 * 20px = 80px
  */
}