You can overwrite this snippet by placing a custom version in site/snippets/email-manager/fields/radio.php.
Modify the CSS classes or structure to match your project’s requirements.
<?php foreach ($options as $key => $label): ?>
<div class="radio-option">
<input type="radio" id="<?= $key ?>" name="<?= $field->name() ?>" value="<?= $key ?>" <?= $field->value() === $key ? 'checked' : '' ?>>
<label for="<?= $key ?>"><?= $label ?></label>
</div>
<?php endforeach; ?>