Add :before element for space before anchors

@angular-router's `scrollOffset` property seems to be
global, so it might mess up something else, and it also
wasn't taking effect when navigating directly to an
anchor anyway (i.e. from browser's address bar).

frontend/src/app/components/docs/api-docs.component.scss

@@ -124,6 +124,14 @@ li.nav-item {
   float: right;
 }
 
+.endpoint-container:before {
+	display: block;
+ 	content: " ";
+  height: 1px;
+  margin-top: -1px;
+  visibility: hidden;
+}
+
 .endpoint-container .section-header {
   display: block;
   background-color: #2d3348;