Rename PostCSS files to .pcss (#9013)

* Rename PostCSS files to `.pcss`

* Make Stylelint happy

* Delint

* Rename new files too

* delint

* Fix bad comment placement

res/css/views/right_panel/_PinnedMessagesCard.pcss

@@ -0,0 +1,68 @@
+/*
+Copyright 2021 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_PinnedMessagesCard {
+    .mx_PinnedMessagesCard_empty_wrapper {
+        display: flex;
+        height: 100%;
+
+        .mx_PinnedMessagesCard_empty {
+            height: max-content;
+            text-align: center;
+            margin: auto 40px;
+
+            .mx_PinnedMessagesCard_MessageActionBar {
+                pointer-events: none;
+                width: max-content;
+                margin: 0 auto;
+
+                // Cancel the default values for non-interactivity
+                position: unset;
+                visibility: visible;
+                cursor: unset;
+
+                &::before {
+                    content: unset;
+                }
+
+                .mx_MessageActionBar_optionsButton {
+                    background: var(--MessageActionBar-item-hover-background);
+                    border-radius: var(--MessageActionBar-item-hover-borderRadius);
+                    z-index: var(--MessageActionBar-item-hover-zIndex);
+
+                    &::after {
+                        background-color: $primary-content;
+                    }
+                }
+            }
+
+            .mx_PinnedMessagesCard_empty_header {
+                color: $primary-content;
+                margin-block: $spacing-24 $spacing-20;
+            }
+
+            > span {
+                font-size: $font-12px;
+                line-height: $font-15px;
+                color: $secondary-content;
+            }
+        }
+    }
+
+    .mx_EventTile_body {
+        word-break: break-word;
+    }
+}