_custom_background_cb() prints background-position in wrong order

[swedish boy]

Even though browser are smart and can take css values (top, left, right) in any order x should come before y for browser compatibility.

https://core.trac.wordpress.org/browser/tags/4.3.1/src/wp-includes/theme.php#L1277

row 1275-1277 says:

              if ( ! in_array( $position, array( 'center', 'right', 'left' ) ) )
                   $position = 'left';
              $position = " background-position: top $position;";

[swissspidy]

According to ​the spec the order isn't relevant.

Note that a pair of keywords can be reordered while a combination of keyword and length or percentage cannot. So ‘center left’ is valid while ‘50% left’ is not.

x should come before y for browser compatibility

Can you elaborate on which browsers don't understand this?