Dashboard export HTML updates

problem_builder/public/css/dashboard.css

@@ -13,7 +13,7 @@
     font-weight: bold;
 }
 
-.pb-dashboard .dashboard-report .avg-row .desc {
+.pb-dashboard .avg-row .desc {
     font-weight: 600;
 }
 

problem_builder/templates/html/dashboard_report.html

@@ -9,6 +9,20 @@
       body {
         font-family: 'Open Sans', 'Helvetica Neue', Helvetica, Arial, sans-serif;
       }
+      .pb-dashboard table {
+          text-align: left;
+      }
+      /* screen reader class from edx-platform */
+      .sr {
+        border: 0;
+        clip: rect(1px 1px 1px 1px);
+        height: 1px;
+        margin: -1px;
+        overflow: hidden;
+        padding: 0;
+        position: absolute;
+        width: 1px;
+      }
       {{css}}
     </style>
   </head>