The style selector in the Ribbon Toolbar functions as an indicator to identify the style of the current text or paragraph. It displays the paragraph and/or text style at the current cursor position or of the currently selected text. For example, in the screenshot below, the cursor is in a paragraph formatted with a style called Body Text:
If the cursor or selection is at a position containing manually-applied formatting the style selector shows the name of the style in bold with a + sign after it, to indicate additional formatting. For example, here the cursor is in text formatted in bold in a paragraph formatted with the Normal style:
Here the cursor is positioned in text
formatted in bold.
The style name is shown as "Normal+" when the cursor is in manually-formatted text . In the rest of the text of the paragraph the style selector display will be "Normal", without the bold highlight and the + sign.
The bold Stylename+ display is also shown when the cursor is in text within a paragraph formatted with a text style, because this also counts as additional formatting:
Here the cursor is in text formatted
with a text style.
If the current paragraph has no style the style selector display will be empty:
The style selector is empty when
the current text has no style.
The style display is also empty when you paste text from Word or another word processor that uses styles. The formatting of the text is imported but the styles with which the text is tagged are not.
If you paste text containing styles that are not defined in your current project the unknown style will be displayed in red in the style selector.
•See Turning formatting into styles for instructions on how to turn imported styles like these into styles you can use in your project.
Dynamic Styles (Reference)