One of the first things you probably when setting up a new site with ClearFusionCMS is to create a stylesheet. Let's assume we have created a stylesheet at /style.css.
To make sure all the same styles are available in the WYSIWYG editor when creating a new document, head to Dashboard > Settings > clearFusionCMS : Content Editing and add /style.css in the Content CCS File field.
That should load all your styles in the toolbar of the WYSIWYG editor when creating a new document.
TIP: When adding or updating a new style to your stylesheet, you will need to reload your stylesheet to add the new styles to the WYSIWYG editor.
If you have any trouble with that because the stylesheet is cached by your browser and CTRL F5 does not work, head to Dashboard > Settings > clearFusionCMS : Content Editing and add ?d=123456789 or some other silly number behind /style.css like this /style.css?d=123456789
That will trick your browser into believing it is not the same file and will force a refresh.
You might also have to reload the page where you are creating or updating a document.