Here you can change the style of the selected text inside a text-element:
Change or remove the style (bold, italic, underlined or crossed out).
Change the font, size and colour of the text.
Change the alignment or define an external link with the '∞' button.
Further down you can change the style of the selected Text-/Foto-/Video-/HTML-element:
Select (checkbox) and define the outline.
Filling only works with text and audio-elements.
Select (checkbox) and define the filling.