diff --git a/plugins/techdocs/src/reader/transformers/styles/rules/extensions.ts b/plugins/techdocs/src/reader/transformers/styles/rules/extensions.ts
new file mode 100644
index 0000000000..403858339e
--- /dev/null
+++ b/plugins/techdocs/src/reader/transformers/styles/rules/extensions.ts
@@ -0,0 +1,91 @@
+/*
+ * Copyright 2022 The Backstage Authors
+ *
+ * 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.
+ */
+
+import { RuleOptions } from './types';
+
+export default ({ theme }: RuleOptions) => `
+/*==================  Extensions  ==================*/
+
+/* HIGHLIGHT */
+.highlight .md-clipboard:after {
+  content: unset;
+}
+
+.highlight .nx {
+  color: ${theme.palette.type === 'dark' ? '#ff53a3' : '#ec407a'};
+}
+
+/* CODE HILITE */
+.codehilite .gd {
+  background-color: ${
+    theme.palette.type === 'dark' ? 'rgba(248,81,73,0.65)' : '#fdd'
+  };
+}
+
+.codehilite .gi {
+  background-color: ${
+    theme.palette.type === 'dark' ? 'rgba(46,160,67,0.65)' : '#dfd'
+  };
+}
+
+/* TABBED */
+.tabbed-set>input:nth-child(1):checked~.tabbed-labels>:nth-child(1),
+.tabbed-set>input:nth-child(2):checked~.tabbed-labels>:nth-child(2),
+.tabbed-set>input:nth-child(3):checked~.tabbed-labels>:nth-child(3),
+.tabbed-set>input:nth-child(4):checked~.tabbed-labels>:nth-child(4),
+.tabbed-set>input:nth-child(5):checked~.tabbed-labels>:nth-child(5),
+.tabbed-set>input:nth-child(6):checked~.tabbed-labels>:nth-child(6),
+.tabbed-set>input:nth-child(7):checked~.tabbed-labels>:nth-child(7),
+.tabbed-set>input:nth-child(8):checked~.tabbed-labels>:nth-child(8),
+.tabbed-set>input:nth-child(9):checked~.tabbed-labels>:nth-child(9),
+.tabbed-set>input:nth-child(10):checked~.tabbed-labels>:nth-child(10),
+.tabbed-set>input:nth-child(11):checked~.tabbed-labels>:nth-child(11),
+.tabbed-set>input:nth-child(12):checked~.tabbed-labels>:nth-child(12),
+.tabbed-set>input:nth-child(13):checked~.tabbed-labels>:nth-child(13),
+.tabbed-set>input:nth-child(14):checked~.tabbed-labels>:nth-child(14),
+.tabbed-set>input:nth-child(15):checked~.tabbed-labels>:nth-child(15),
+.tabbed-set>input:nth-child(16):checked~.tabbed-labels>:nth-child(16),
+.tabbed-set>input:nth-child(17):checked~.tabbed-labels>:nth-child(17),
+.tabbed-set>input:nth-child(18):checked~.tabbed-labels>:nth-child(18),
+.tabbed-set>input:nth-child(19):checked~.tabbed-labels>:nth-child(19),
+.tabbed-set>input:nth-child(20):checked~.tabbed-labels>:nth-child(20) {
+  color: var(--md-accent-fg-color);
+  border-color: var(--md-accent-fg-color);
+}
+
+/* TASK-LIST */
+.task-list-control .task-list-indicator::before {
+  background-color: ${theme.palette.action.disabledBackground};
+}
+.task-list-control [type="checkbox"]:checked + .task-list-indicator:before {
+ background-color: ${theme.palette.success.main};
+}
+
+/* ADMONITION */
+.admonition {
+  font-size: var(--md-typeset-font-size) !important;
+}
+.admonition .admonition-title {
+  padding-left: 2.5rem !important;
+}
+
+.admonition .admonition-title:before {
+  top: 50% !important;
+  width: 20px !important;
+  height: 20px !important;
+  transform: translateY(-50%) !important;
+}
+`;