Simply specify <code>CupertinoPickerDefaultSelectionOverlay</code> for the <code>selectionOverlay</code> property.
<div class="code-block-container"><pre class="shiki github-dark" style="background-color:#151e2c;color:#e1e4e8"><code class="code-line" data-line="1">CupertinoPicker(
 ...
 selectionOverlay: const CupertinoPickerDefaultSelectionOverlay(background: Colors.transparent),
 ...
),
</code></pre></div><h2 id="reference" data-line="9" class="code-line">
<a class="header-anchor-link" href="#reference" aria-hidden="true"></a> Reference</h2>
<iframe id="zenn-embedded__211aaaaefd1e4" src="https://embed.zenn.studio/card#zenn-embedded__211aaaaefd1e4" data-content="https%3A%2F%2Fstackoverflow.com%2Fquestions%2F66703336%2Fhow-to-remove-grey-box-from-picker-flutter-widget" frameborder="0" scrolling="no" loading="lazy"></iframe><a href="https://stackoverflow.com/questions/66703336/how-to-remove-grey-box-from-picker-flutter-widget" style="display:none" target="_blank" rel="nofollow noopener noreferrer">https://stackoverflow.com/questions/66703336/how-to-remove-grey-box-from-picker-flutter-widget</a>

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[Flutter] How to remove the gray box from CupertinoPicker

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