Use monospaced font and fix padding for reply placeholder

app/assets/stylesheets/pages/note_form.scss

@@ -304,12 +304,13 @@ table {
   }
 
   .reply-placeholder-text-field {
+    font-family: $monospace-font;
+    font-size: 13px;
     border-radius: $gl-border-radius-base;
     width: 100%;
     resize: none;
-    padding: $gl-padding-4 $gl-padding;
+    padding: $gl-padding-4 $gl-padding-12;
     border-color: $border-color;
-    color: $gray-darkest;
     background-color: $white;
 
     @include media-breakpoint-down(xs) {