Add styles for next last page in textbook

lms/static/sass/course/_textbook.scss

@@ -72,25 +72,41 @@ div.book-wrapper {
             @include box-sizing(border-box);
             height: 100%;
             width: 100%;
-            padding-top: 200%;
             vertical-align: middle;
             @include transition;
-            background: rgba(#000, .7);
+            background-color: rgba(#000, .7);
+            background-repeat: no-repeat;
+            background-position: center;
             opacity: 0;
             filter: alpha(opacity=0);
+            text-indent: -9999px;
 
             &:hover {
               opacity: 1;
               filter: alpha(opacity=100);
+
+              &.last {
+              }
+
+              &.next {
+              }
             }
           }
 
           &.last {
             left: 0;
+
+            a {
+              background-image: url('../images/textbook/textbook-left.png');
+            }
           }
 
           &.next {
             right: 0;
+
+            a {
+              background-image: url('../images/textbook/textbook-right.png');
+            }
           }
 
         }