Fix techdocs nav positioning when using blog plugin

Signed-off-by: Jackson Chen <jacksonc@spotify.com>

.changeset/curvy-sheep-grab.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-techdocs': patch
+---
+
+Fixes left navigation positioning when using mkdocs blog plugin

plugins/techdocs/src/reader/transformers/styles/rules/layout.ts

@@ -121,6 +121,10 @@ export default ({ theme, sidebar }: RuleOptions) => `
   margin-bottom: 50px;
 }
 
+.md-content > .md-sidebar {
+  left: 16rem;
+}
+
 .md-footer {
   position: fixed;
   bottom: 0px;