[Plugin: Genesis Single Post Navigation] CSS stylings not working

Hi — I was trying to make some edits to the way the arrows look and tried to follow the directions to add an “additions” file to my root folder. I’m running Genesis/Lifestyle, so I put it in the Lifestyle root folder. I wanted to change the arrows to be smaller, lower down, and to match the other grays on the site, so I put this code in the additions file — but it doesn’t seem to have worked. Where did I go wrong? Thanks!

/*
GSPN Additions
*/

#gspn-prevpost a, #gspn-nextpost a, #gspn-prevpost-reverse a, #gspn-nextpost-reverse a {
border-bottom: medium none;
border-top: medium none;
color: #E5E5E5;
font-size: 50px;
line-height: 105px;
padding-bottom: 15px;
position: fixed;
text-align: center;
top: 72%;
vertical-align: middle;
width: 80px;
}

http://wordpress.org/extend/plugins/genesis-single-post-navigation/