wire up editor component (somewhat hacky)

res/css/_components.scss

@@ -89,6 +89,7 @@
 @import "./views/elements/_InlineSpinner.scss";
 @import "./views/elements/_ManageIntegsButton.scss";
 @import "./views/elements/_MemberEventListSummary.scss";
+@import "./views/elements/_MessageEditor.scss";
 @import "./views/elements/_PowerSelector.scss";
 @import "./views/elements/_ProgressBar.scss";
 @import "./views/elements/_ReplyThread.scss";

res/css/views/elements/_MessageEditor.scss

@@ -0,0 +1,42 @@
+/*
+Copyright 2019 Vector Creations Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+.mx_MessageEditor {
+    border-radius: 4px;
+    background-color: #f3f8fd;
+    padding: 10px;
+
+    .editor {
+        border-radius: 4px;
+        border: solid 1px #e9edf1;
+        background-color: #ffffff;
+    }
+
+    .buttons {
+        display: flex;
+        flex-direction: column;
+        align-items: end;
+        padding: 5px 0;
+
+        .mx_AccessibleButton {
+            background-color: $button-bg-color;
+            border-radius: 4px;
+            padding: 5px 40px;
+            color: $button-fg-color;
+            font-weight: 600;
+        }
+    }
+}

res/css/views/messages/_MessageActionBar.scss

@@ -69,6 +69,10 @@ limitations under the License.
     mask-image: url('$(res)/img/reply.svg');
 }
 
+.mx_MessageActionBar_editButton::after {
+    mask-image: url('$(res)/img/edit.svg');
+}
+
 .mx_MessageActionBar_optionsButton::after {
     mask-image: url('$(res)/img/icon_context.svg');
 }