Add arrows via css

aleksis/core/static/style.scss

@@ -387,6 +387,50 @@ table.striped > tbody > tr:nth-child(odd), table tr.striped, table tbody.striped
   background-color: rgba(208, 208, 208, 0.5);
 }
 
+th.orderable > a {
+  color: rgba(0, 0, 0, 0.6);
+  display: block;
+  width: inherit;
+  height: inherit;
+}
+
+th.orderable > a::after {
+  @extend i.material-icons;
+  font-family: 'Material Icons';
+  font-weight: normal;
+  font-style: normal;
+  font-size: 24px;
+  display: inline-block;
+  line-height: 1;
+  text-transform: none;
+  letter-spacing: normal;
+  word-wrap: normal;
+  white-space: nowrap;
+  direction: ltr;
+  -webkit-font-smoothing: antialiased;
+  text-rendering: optimizeLegibility;
+  -moz-osx-font-smoothing: grayscale;
+  font-feature-settings: 'liga';
+  float: right;
+  content: "unfold_more";
+}
+
+th.orderable.asc > a {
+  color: inherit;
+
+  &::after {
+    content: "expand_less";
+  }
+}
+
+th.orderable.desc > a {
+  color: inherit;
+
+  &::after {
+    content: "expand_more";
+  }
+}
+
 /*+++++++*/
 /* Print */
 /*+++++++*/