GC-611: adjust styles for CodeMirror of HackMD

resource/styles/hackmd/style.scss

@@ -13,3 +13,9 @@
     display: none;
   }
 }
+
+.CodeMirror pre {
+  font-family: Osaka-Mono, "MS Gothic", Monaco, Menlo, Consolas, "Courier New", monospace;
+  font-size: 14px;
+  line-height: 20px;
+}