Just brushing the surface of the Speed Force, Bart accessed his super speed-- not to move or run... but rather because this was one of the very few moments that he wanted to last as long as possible.
When the kiss finally broke with the little pecks at the end, Bart put his super speed aside again and smiled at Kara bashfully, his cheeks red.
"Yeah. Wow." He agreed, "That was... really..." He didn't know what it was, "...awesome."