<ul id="social-menu">
  <li>
    <a href="#">
      <img src="img/icons/facebook.svg" alt="facebook">
     </a>                            
  </li>
</ul>

 #about-section #social-menu {
  margin-top: 30px; }

#about-section #social-menu li {
  display: inline;
  list-style-type: none;
  padding-right: 10px;
  margin: 0; }

#about-section #social-menu a {
  opacity: 0.7; 
  transition: all 0.3s;}

#about-section #social-menu a:hover {
  opacity: 1; 
  transition: all 0.3s;}