"How to Build a Website", trouble getting the nav a to work in CSS

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

/**************
GERNERAL 
**************/

body {
  font-family: 'Open Sans', sans-serif; 
}

#wrapper {
max-width: 940px;
  margin: 0 auto;
  padding: 0 5%;
   }

a {
 text-decoration:none; 
}

img {
  max-width: 100%; 
}

/**************
HEADING  
**************/

/*controling the pixels goes top, right, bottom, left
-Setting our margins keeps the header separated from other content at least on the bottom. But removes the problematic margins that we had on the top, previously.
-Adding padding on top will seperate the text without actually removing the margin from the top of the page. 
-It's now a floated element which means it doesn't have an explicit width anymore. We want to specifically say that this element should stretch across the entire page so we've set a width of 100%.
*/
header {
  float: left;
  margin: 0 0 30px 0; 
  padding: 5px 0 0 0;
  width: 100%;
}

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

h1 {
 font-family: 'Changa One', sans-serif; 
  font-family: 15px 0; 
  font-size: 1.75em; 
}

h2 {
  font-size: 0.75em;
  margin: -5px 0 0;
  font-weight: normal;
}


/**************
NAV
**************/
nav {
  text-align: center;
  padding: 10px 0;
  margin: 20px 0 0
}

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

nav li {
display: inline-block; 
}

nav a {
  font-weight:800;
  padding: 15px 10px;
}
/**************
FOOTER
**************/
 footer { 
  font-size: 0.75em;
  text-align: center;
  clear:both; 
  padding-top: 50px;
  color: #ccc;
}

.social-icon {
  width: 20px;
  height: 20px;
  margin: 0 5px;
}



/**************
PAGE: PORTFOLIO   
**************/
#gallery {
  margin: 0;
  padding: 0;
  list-style: none;
}

/* the width of the pictures are at a max of 45% of the browser, no matter the size of the browser window. So it works with mobile. Since 45 and 45 is 90, we have a remainder of 10 to use for margins. 2.5% on each side of the two pictures. */

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

#gallery li a p {
  margin: 0;
  padding: 5%;
  font-size: 0.75em;
  color: #bdc3c7;
}
/**************
COLORS  
**************/

/* site body THIS IS A COMMENT*/
body {
  background-color: #fff;
  color: #999;
}

/* green header */
header {
  background:#6ab47b;
  border-color: #599a68;
}

/* nav background on mobile */ 
nav {
  background: #599a68;
}

/*logo text*/
h1, h2 {
  color: #fff;
}

a {
 color: #6ab47b; 
}

/* nav link */
nav a, nav a:visited {
  color:#fff;
}

/*selected nav link*/
nav a.selected, nav a:hover {
  color: #32673f; 
}