How do I add a combinator to my style?
You can only add combinators to child selectors. Add a child selector and combinator will appear in the Style tree.
Acquia Cohesion renames to Site Studio from version 6.2. Tell me more.
You don't. You apply a Descendant selector. These use a (Space).
Modifiers allow you to apply styles to an element when a specific class, id or attribute is present.
The Youtube video embed is responsive so it should expand to the width of its parent. If you do need to set a width you can apply the Width CSS property through the Style Builder.
The WYSIWYG (ckeditor) adds a paragraph tag around the text within the block quote. This causes it to inherit the text size of your paragraph base style.