*, * {
  box-sizing: border-box;
}

nav {
  display: flex;
  flex-direction: column;
  height: 100%;
  width: 100%;
  background-color: beige;
}

nav img {
  width:140px;
  height:100px;
}

nav a,
nav a:link {
  text-decoration: none;
  color: green;
  border-bottom: 2px solid green;
  width: 100%;
  padding: 5px;
  display: block;
}

nav a:hover {
  font-weight: bolder;
}

nav a:visited {
  color: green;
}

.nav-verein {
 /* display: none;*/
 margin-left:10px;
 width: calc(100% - 10px);
}

.sub-menu:hover .nav-verein, 
.sub-menu:focus .nav-verein {
  display: flex;
}


@media screen and (max-device-width: 480px) {
  nav a,
  nav a:link {
    font-size: 60px;
  }

  nav img {
    width: 50%;
    height: auto;
  }
}