Why is it showing "Bummer!Did you set the background-size to 20px?"

a {
  text-decoration: none;
}

#wrapper {
  max-width: 940px;
  margin: 0 auto;
}

#logo {
  text-align: center;
  margin: 0;
}

h1, h2 {
  color: #fff;
}

nav a {
  color: #fff;
}

nav a:hover {
  color: #32673f;
}

h1 {
  font-family: ‘Changa One’, sans-serif;
  font-size: 1.75em;
  font-weight: normal;
}

img {
  max-width: 100%;
}

#gallery {
  margin: 0;
  padding: 0;
  list-style: none;
}

#gallery li {
  float: left;
  width: 45%;
  margin: 2.5%;
  background-color: #f5f5f5;
  color: #bdc3c7;
}

nav ul {
  list-style: none;
  margin: 0 10px;
  padding: 0;
}

nav li {
  display: inline-block;
}

nav a {
  font-weight: 800;
  padding: 15px 10px;
}

.profile-photo {
  display: block;
  margin: 0 auto 30px;
      max-width: 150px;
  border-radius: 100%;
}

ul.contact-info{
  font-size:0.9em;
  margin:0;
  padding:0;
  list-style:none;
}

.contact-info a{
  display:block;
  min-height:20px;
  background-repeat:no-repeat;
  background-size:20px;
  padding:0 0 0 30px;
}