add IconButton as in design

res/css/views/elements/_IconButton.scss

@@ -0,0 +1,55 @@
+/*
+Copyright 2019 The Matrix.org Foundation C.I.C.
+
+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_IconButton {
+    width: 32px;
+    height: 32px;
+    border-radius: 100%;
+    background-color: $accent-bg-color;
+    // don't shrink or grow if in a flex container
+    flex: 0 0 auto;
+
+    &.mx_AccessibleButton_disabled {
+        background-color: none;
+
+        &::before {
+            background-color: lightgrey;
+        }
+    }
+
+    &:hover {
+        opacity: 90%;
+    }
+
+    &::before {
+        content: "";
+        display: block;
+        width: 100%;
+        height: 100%;
+        mask-repeat: no-repeat;
+        mask-position: center;
+        mask-size: 55%;
+        background-color: $accent-color;
+    }
+
+    &.mx_IconButton_icon_check::before {
+        mask-image: url('$(res)/img/feather-customised/check.svg');
+    }
+
+    &.mx_IconButton_icon_edit::before {
+        mask-image: url('$(res)/img/feather-customised/edit.svg');
+    }
+}