<flux:input-group> that includes <flux:select variant="combobox"> and radii behaviour

[oMikeo]

Border radii are not adjusted for comboboxes inside input groups.

To reproduce:

<flux:field>
    <flux:label>Email address</flux:label>
    <flux:description>Enter the first part of the email address only.</flux:description>
    <flux:input.group>
        <flux:input type="text" icon-trailing="at-symbol"/>
        <flux:select variant="combobox">
            <flux:option value="a" selected>domain.com</flux:option>
            <flux:option value="b">domain.net</flux:option>
            <flux:option value="c">domain.org</flux:option>
            <flux:option value="d">domain.io</flux:option>
            <flux:option value="e">domain.dev</flux:option>
        </flux:select>
    </flux:input.group>
</flux:field>

Works fine with both default select and with variant="listbox"