BJlaDuMup

header .wrapper {
  display: flex;
  justify-content: space-between;
}
nav {
  margin-top: 54px;
  margin-left: 20%; - удалить
}
.topnav a {
  margin-right: 70px; - поменять на margin-left
....

#footer {
    position: relative;
    bottom: 0;
}