Hello,

I saw the screenshot you attached.

Please try adding the following Custom CSS in the Global Custom CSS area under Theme Settings >> Custom CSS.

.elementor-swiper-button.elementor-swiper-button-prev, .elementor-swiper-button.elementor-swiper-button-next {
    font-size: 20px;
    color: white;
    background: blue;
    padding: 15px;
}

Regards.
Xtemos Studios