Why is the preview in the Style builder not updating?
The style preview may not be updated because the refresh icon hasn't been toggled to the active state.
Acquia Cohesion renames to Site Studio from version 6.2. Tell me more.
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.