On phones the location-picker modal is a full-screen sheet sized with
height: 100vh. On iOS Safari 100vh is the large-viewport height (measured
as if the browser toolbars were retracted), so while the toolbars are
showing the bottom of the sheet — the footer with the 'Use this location'
button — falls behind Safari's chrome and is cut off.
Size the sheet with 100dvh (dynamic viewport height), which tracks the
currently-visible height. The flex map yields the space so the footer
stays on screen. 100vh is kept as a fallback for older engines, and the
footer gains safe-area-inset-bottom padding to clear the home indicator
once the bottom toolbar retracts.