Lengthen the "screen-per-page" input box to prevent cutoff caused by setting...

Lengthen the "screen-per-page" input box to prevent cutoff caused by setting type="number", remove some duplicate css, props thezman84, see #20015

git-svn-id: https://core.svn.wordpress.org/trunk@20571 1a063a9b-81f0-0310-95a4-ce76da25c4cd