Nǐ jīntiān zhēn piàoliɑnɡ.

你今天真漂亮。

You're so beautiful today.
Notes:

你(nǐ): you

今天(jīntiān): today

真(zhēn): really

漂亮(piàoliɑnɡ): beautiful, pretty

Example:

A：你今天真漂亮。

     Nǐ jīntiān zhēn piàoliɑnɡ.

     You're so beautiful today.

B：谢谢。

     Xièxie.

     Thank you.