init monospace fonts

src/client/styles/hackmd/style.scss

@@ -14,8 +14,8 @@
   }
 }
 
-.CodeMirror pre {
-  font-family: Osaka-Mono, "MS Gothic", Monaco, Menlo, Consolas, "Courier New", monospace;
+.CodeMirror pre.CodeMirror-line {
+  font-family: Osaka-Mono, 'MS Gothic', Monaco, Menlo, Consolas, 'Courier New', monospace;
   font-size: 14px;
   line-height: 20px;
 }

src/client/styles/scss/_editor-overlay.scss

@@ -69,6 +69,6 @@
 
 .modal-gfm-cheatsheet .modal-body {
   .hljs {
-    font-family: monospace;
+    font-family: $font-family-monospace;
   }
 }

src/client/styles/scss/_on-edit.scss

@@ -304,7 +304,7 @@ body.on-edit {
 }
 
 // overwrite .CodeMirror pre
-.CodeMirror pre {
+.CodeMirror pre.CodeMirror-line {
   font-family: $font-family-monospace;
 }