There are a few things that could cause the issue, or I should say a combination of things. With the formatting problems, you might have the “!important css” declaration overriding your CSS from the page/post editor.
Here is an example:
.post {
font-family:Verdana, sans-serif;
font-size:14px !important;
}
Or I want to add a break so that text
appears on different lines
This could be a few issues, the best way to correct it is to use the plug-in TinyMce Advanced
Install the plugin, then go to Appearance>TinyMce, in the options that appear towards the bottom of the screen select the check-box that says Stop removing p tags. You can also check the box that says import editor style. If your theme has a specific file for the editor it will be used, if not it will try to emulate the css of your theme automatically.
See the image for the TinyMce Settings:
