apply markdown block styles to rendered text media-tags

customize.dist/src/less2/include/markdown.less

@@ -52,13 +52,6 @@
             text-overflow: ellipsis;
         }
     }
-
-    div.plain-text-reader {
-        background: @cp_markdown-bg;
-        padding: 10px;
-        color: black;
-        text-align: left;
-    }
 }
 
 .mediatag_cryptpad() {
@@ -154,6 +147,13 @@
         color: @cryptpad_text_col;
         background-color: @cp_markdown-block-bg;
     }
+
+    div.plain-text-reader {
+        background: @cp_markdown-block-bg;
+        padding: 10px;
+        color: @cp_markdown-block-fg;
+        text-align: left;
+    }
 }
 
 .markdown_cryptpad() {