The Toolbar search field, when the Toolbar is displayed on the frontend, might
inherit CSS properties from the active Theme stylesheet. For example, this
happened with Twenty Seventeen that sets `display: block;` on all the input
fields. Thus, there's the need to reset some CSS properties to avoid inheritance.
Props @sagarprajapati.
Fixes#40313.
Built from https://develop.svn.wordpress.org/trunk@40418
git-svn-id: http://core.svn.wordpress.org/trunk@40316 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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