Styling updates to sidebar to match design

app/assets/stylesheets/pages/boards.scss

@@ -279,8 +279,38 @@ lex
   }
 }
-.right-sidebar.issue-boards-sidebar {
+.issue-boards-sidebar {
+  &.right-sidebar {
     position: absolute;
     top: 0;
     bottom: 0;
   }
+
+  .issuable-sidebar-header {
+    position: relative;
+  }
+
+  .gutter-toggle {
+    position: absolute;
+    top: 0;
+    bottom: 10px;
+    right: 0;
+    width: 22px;
+    color: $gray-darkest;
+
+    .fa {
+      position: absolute;
+      top: 50%;
+      margin-top: (-15px / 2);
+    }
+  }
+
+  .issuable-header-text {
+    width: 100%;
+    padding-right: 35px;
+
+    > strong {
+      font-weight: 600;
+    }
+  }
+}

app/views/projects/boards/components/_sidebar.html.haml

@@ -13,7 +13,7 @@
         %a.gutter-toggle.pull-right{ role: "button",
           href: "#",
           "@click" => "closeSidebar",
-          aria: { label: "Toggle sidebar" } }
+          "aria-label" => "Toggle sidebar" }
           = icon("times")
       .js-issuable-update
         = render "projects/boards/components/sidebar/assignee"