Hmm, libxml seems to not like double quotes, weird, this version tested

//*[
    (
        name() = 'para'
        or
        name() = 'header'
    )
    and
    (
        not(descendant::*)
    )
    and
    (
        contains(
            translate(
                .,
                'DESIGN',
                'design'
            ),
            'design'
        )
    )
]
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