Smarty Error: [in Tpl_body:21 Line 21]: Using CSS 'WITHIN' A Smarty Template?

Using CSS 'WITHIN' a Smarty Template? - smarty error: [in tpl_body:21 line 21]:

Hello,

To use a particular command (CSS) once in a Smarty template - How can I do? - In addition to the display configuration / CSS in an external file?

EC: - tr: hover (color = blue;)

Of course, there is no command "color Smarty, causing an error ...

Please advise - Thanks