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/dialogs/_CompoundDialog.pcss

@@ -0,0 +1,82 @@
+/*
+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.
+*/
+
+// --------------------------------------------------------------------------------
+// DEV NOTE: This stylesheet covers dialogs listed by the compound, including
+// over multiple React components. The actual inner contents of the dialog should
+// be in their respective stylesheets.
+// --------------------------------------------------------------------------------
+
+// Override legacy/default styles for dialogs
+.mx_Dialog_wrapper.mx_CompoundDialog > .mx_Dialog {
+    padding: 0; // we'll manage it ourselves
+    color: $primary-content;
+}
+
+.mx_CompoundDialog {
+    .mx_CompoundDialog_header {
+        padding: 32px 32px 16px 32px;
+
+        h1 {
+            display: inline-block;
+            font-weight: 600;
+            font-size: $font-24px;
+            margin: 0; // managed by header class
+        }
+
+        .mx_CompoundDialog_cancelButton {
+            @mixin customisedCancelButton;
+            width: 20px;
+            height: 20px;
+
+            // Align with middle of title, 34px from right edge
+            position: absolute;
+            top: 34px;
+            right: 34px;
+        }
+    }
+
+    .mx_CompoundDialog_content {
+        overflow: auto;
+        padding: 8px 32px;
+    }
+
+    .mx_CompoundDialog_footer {
+        padding: 20px 32px;
+        text-align: right;
+        position: absolute;
+        bottom: 0;
+        left: 0;
+        right: 0;
+
+        .mx_AccessibleButton {
+            margin-left: 24px;
+        }
+    }
+}
+
+.mx_ScrollableBaseDialog {
+    width: 544px; // fixed
+    height: 516px; // fixed
+
+    .mx_CompoundDialog_content {
+        height: 349px; // dialogHeight - header - footer
+    }
+
+    .mx_CompoundDialog_footer {
+        box-shadow: 0px -4px 4px rgba(0, 0, 0, 0.05); // hardcoded colour for both themes
+    }
+}