Prevent date inputs shifting alignment on iOS 18

Due to an upstream issue in Safari on iOS 18 (and potentially 17), the box model calculations for these inputs go iffy when the value is deleted and re-typed.

The upstream issue was reported during the beta period of iOS 26 and fixed in the release of iOS 26 in September, however no fix for older versions seems to be coming, so we should prevent the issue in our own code in the meantime.

NHS.UK Frontend issue: nhsuk/nhsuk-frontend#1227
Our bug report: alphagov/reported-bugs#90

Author: querkmachine

CHANGELOG.md

@@ -4,6 +4,12 @@ For advice on how to use these release notes, see [our guidance on staying up to
 
 ## Unreleased
 
+### Fixes
+
+We've made fixes to GOV.UK Frontend in the following pull requests:
+
+- [#6454: Prevent date inputs shifting alignment on iOS 18](https://github.com/alphagov/govuk-frontend/pull/6454) – thanks to @rowellx68 for reporting this issue and @colinrotherham for suggesting the fix.
+
 ## v6.0.0-beta.1 (Beta breaking release)
 
 ### Breaking changes

packages/govuk-frontend/src/govuk/components/date-input/_index.scss

@@ -14,6 +14,11 @@
     display: inline-block;
     margin-right: govuk-spacing(4);
     margin-bottom: 0;
+
+    // Prevents an issue in iOS Safari 18 where the items vertically
+    // shift when the value of inputs is changed.
+    // https://github.com/alphagov/reported-bugs/issues/90
+    vertical-align: bottom;
   }
 
   .govuk-date-input__label {