MDL-46950 gradereport_grader: Prettier styling for base and clean

This issue is a part of the MDL-46658 Task.
This issue is a part of the MDL-25544 Epic.

grade/report/grader/styles.css

@@ -42,6 +42,13 @@
     vertical-align: middle;
 }
 
+/**
+ * Stripped table.
+ */
+.gradeparent tr:nth-of-type(even) .cell {
+    background-color: #f9f9f9;
+}
+
 /**
  * All the floating divs.
  */
@@ -53,14 +60,20 @@
 }
 
 /**
- * All the header/floating cells.
+ * All the headers + floating cells.
  */
 .gradeparent .heading .cell,
 .gradeparent .avg .cell,
 .gradeparent .user.cell {
     font-size: 14px;
     font-weight: normal;
-    background-color: #eee;
+}
+
+/**
+ * All the floating cells.
+ */
+.gradeparent .floater .cell {
+    background-color: #f9f9f9;
 }
 
 /**

theme/bootstrapbase/less/moodle/grade.less

@@ -230,3 +230,22 @@
         }
     }
 }
+
+/**
+ * Grader report.
+ */
+.path-grade-report {
+    .gradeparent {
+        table {
+            .border-radius(@baseBorderRadius);
+        }
+        table,
+        .cell {
+            border-color: @tableBorder;
+        }
+        tr:nth-of-type(even) .cell,
+        .floater .cell {
+            background-color: @tableBackgroundAccent;
+        }
+    }
+}