mol-plugin: use monospace font for sequence

src/mol-plugin/skin/base/components/sequence.scss

@@ -20,6 +20,10 @@
     overflow-y: auto;
     overflow-x: hidden;
     font-size: 90%;
+
+    .msp-sequence-wrapper-non-empty {
+        font-family: monospace;
+    }
 }
 
 .msp-sequence-wrapper {

src/mol-plugin/ui/sequence.tsx

@@ -297,7 +297,7 @@ export class SequenceView extends PluginUIComponent<{ }, SequenceViewState> {
             </div>
 
             {typeof sequenceWrapper === 'string'
-                ? <div className='msp-sequence-wrapper'>{sequenceWrapper}</div>
+                ? <div className='msp-sequence-wrapper msp-sequence-wrapper-non-empty'>{sequenceWrapper}</div>
                 : <Sequence sequenceWrapper={sequenceWrapper} />}
         </div>;
     }

src/mol-plugin/ui/sequence/sequence.tsx

@@ -104,7 +104,7 @@ export class Sequence<P extends SequenceProps> extends PluginUIComponent<P, Sequ
         }
 
         return <div
-            className='msp-sequence-wrapper'
+            className='msp-sequence-wrapper msp-sequence-wrapper-non-empty'
             onContextMenu={this.contextMenu}
             onMouseDown={this.mouseDown}
         >