The zoomed page fills the window again (width was divided twice)

Zooming left the page filling four fifths of the window, and less as the
zoom went up: at 1.6 it sat in the left three fifths with the rest of the
window empty.

body carried width:calc(100%/zoom). Under CSS zoom a percentage already
resolves against the containing block in the zoomed element's own units,
so 100% is the full width and dividing it again shrank the page by the zoom
a second time. A block fills its container without being told to, so the
declaration is gone. Viewport units are the exception -- dvh does not know
about zoom -- which is why the height still has to be divided back out.

Measured at 1.25, 1.6 and 2: body is exactly the window's 2275 by 1427 in
each, and the document overflows by nothing in either direction. The first
time round only the overflow was checked, which a page that under-fills
passes just as happily as one that fits.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ios/Sources/WebViewController.swift

@@ -100,10 +100,12 @@ final class WebViewController: UIViewController, WKNavigationDelegate {
         /// CSS zoom is part of layout, so the page measures itself correctly; body's own width
         /// and height are divided back out because its containing block is not zoomed.
         static func script(_ zoom: Double) -> String {
-            let css = zoom == 1
-                ? ""
-                : "body{zoom:\(zoom);width:calc(100%/\(zoom))!important;"
-                  + "height:calc(100dvh/\(zoom))!important}"
+            // No width. A percentage resolves against the containing block in the zoomed
+            // element's own units, so 100% is already the full width -- dividing it again left
+            // the page filling four fifths of the window and then three fifths as the zoom went
+            // up. A block fills its container by itself. dvh is the exception: viewport units do
+            // not know about zoom, so the height does have to be divided back out.
+            let css = zoom == 1 ? "" : "body{zoom:\(zoom);height:calc(100dvh/\(zoom))!important}"
             return "(function(){var id='ipx-zoom';var s=document.getElementById(id);"
                 + "if(!s){s=document.createElement('style');s.id=id;"
                 + "(document.head||document.documentElement).appendChild(s)}"