Not seeing "clear: left" on nth-child (4n) of my responsive CSS

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%;
}

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

.contact-info a {
  display: block;
  min-height: 20px;
  background-repeat: no-repeat;
  background-size: 20px 20px;
  padding: 0 0 0 30px;
  margin: 0 0 10px;
}


@media screen and (min-width: 480px) {

/******************************
TWO COLUMN LAYOUT
*******************************/


#primary {
  width: 50%;
  float: left;
 }

#secondary {
  width: 40%;
  float: right;
  }



/******************************
PAGE: PORTFOLIO
*******************************/

#gallery li {
    width: 28.3333%; 
  }

  #gallery li:nth-child (4n) {
    clear: left;
  }





/******************************
PAGE: ABOUT
*******************************/

.profile-photo {
  float: left;
  margin: 0 5% 80px 0;
  }
}



@media screen and (min-width: 660px)  {



/******************************
HEADER
*******************************/  

  nav {
    background: none;
    float: right;
    font-size: 1.125em;
    margin-right: 5%;
    text-align: right;
    width: 45%;
  }  

  #logo {
    float: left;
    margin-left: 5%;
    text-align: left;
    width: 45%;
  }

 h1 {
    font-size: 2.5em; 
 }

 h2 {
    font-size: 0.825em;
    margin-bottom: 20px;
 }

 header{
    border-bottom: 5px solid #599a68;
    margin-bottom: 60px;
 }

}