Disables the previous/next arrows on pdf books on the first/last pages respectively

common/static/js/pdfviewer.js

@@ -200,6 +200,12 @@ PDFJS.disableWorker = true;
             document.getElementById('numPages').textContent = 'of ' + pdfDocument.numPages;
             $("#pageNumber").max = pdfDocument.numPages;
             $("#pageNumber").val(pageNum);
+
+            // Enable/disable the previous/next buttons
+            if (pageNum > 1) $("#previous").addClass("enabled");
+            else $("#previous").removeClass("enabled");
+            if (pageNum < pdfDocument.numPages) $("#next").addClass("enabled");
+            else $("#next").removeClass("enabled");
         }
 
         // Go to previous page

lms/static/sass/course/_textbook.scss

@@ -160,12 +160,12 @@ div.book-wrapper {
             @include transition(none);
             vertical-align: middle;
             width: 100%;
+          }
 
-            &:hover {
+          a.enabled:hover {
             opacity: 1.0;
             filter: alpha(opacity=100);
           }
-          }
 
           &.last {
             left: 0;