Headers sit at the right height, overlay icons in the right place

Two layout fixes for the furniture around a page's content. A row of controls - a search box, buttons, a logo - centred in a header no longer makes the header taller than it should be: the engine now measures each control by its real height instead of a one-line guess. And overlay icons sit where they belong: the common pattern that floats a magnifier or a clear button inside a search box used to drift the icon out of its box (so it went missing or clipped); it now centres correctly, matching other browsers.