Remove Inner Border on Single Sliders

Hi

We're using the slideshow on several pages to show a single testimonial which transitions. For example: https://www.zemaitis-uk.com/

We'd previously used additional CSS to remove the inner border (i.e. only showing the outer blue radius border):

.strong-view.wpmtst-default .wpmtst-testimonial-inner {
    border: none;
}

Since some recent updates the inner grey border has reappeared. We've tried using inspect to identify new CSS but have been successful.

Can you please advise what CSS to use in customizer to remove the inner grey square border.

Many thanks!

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