Style

Style[expr,options] displays with expr formatted using the specified option settings. 

Style[expr,"style"] uses the option settings for the specified style in the current notebook. 

Style[expr,color] displays using the specified color. 

Style[expr,Bold] displays with fonts made bold. 

Style[expr,Italic] displays with fonts made italic. 

Style[expr,Underlined] displays with fonts underlined. 

Style[expr,Larger] displays with fonts made larger. 

Style[expr,Smaller] displays with fonts made smaller. 

Style[expr,n] displays with font size n. 

Style[expr,Tiny], Style[expr,Small], etc. display with fonts that are tiny, small, etc. 

Please visit the official Wolfram Language Reference for more details and examples on core symbols.