Vector: Set media screen on styles.less

This prevents the styles from overriding the print stylesheet.
Follows-up Ica0b69ad950, which removed it.

Bug: 56366
Change-Id: I3979a90f828ff808deae2f7fcc5c1dd7e83e9b67
(cherry picked from commit 98ef2d9b7e0290bd33378007fd4d45a7d60da1ab)