To fix this, as covered here, go to Debug -> Open Preferences File and add these as XML types within the JSON structure. ncx files, you will notice that there is no syntax highlighting. In the Table of Contents Options window, next to each available style you want to use (these are Word’s built-in styles starting. In the Table of Contents window that opens, click the Options button. For example, if you're going through your HTML and you decide you want to change the style on something, just highlight the tag or the class attribute and activate Quick Edit (Cmd+E on OSX) and you can immediately edit the CSS styles, even if it's in a different file! Super convenient. On the dropdown menu when you click the Table of Contents button, choose the Custom Table of Contents option. Why do this? Because Brackets has some pretty neat features.
(Not totally accurate rendering, compared to how it'll look on an eReader, but suitable.)
As a suggestion, I have been enjoying using Brackets to create epubs on my Mac.
