This causes a style regression reported in bug 19219; change appears to have been made due to mistaken impression of what the code did?
Explanation: "padding: 0 .9em" sets the top/bottom padding to 0 and the left/right padding to 0.9em.
"padding-top: 0.9em" sets the top padding to 0.9em and leaves the top/left/right padding unset -- totally different.
I'm changing it to "padding: 0 0.9em" to make it clearer that it's not a mistake for "0.9".