Thank you for providing the link.
Viewing your website, I can confirm that the layout of this Log in/Sign up button is indeed set through the plugin you’re using.
With that said, it would be best to reach out to them for assistance regarding this.
Otherwise, if you would like to overwrite the layout through custom code, here is a CSS you may try adding in Appearance > Customize > Additional CSS:
@media (max-width: 768px) {
ubermenu .ubermenu-item-layout-image_left>.ubermenu-target-text {
padding-left: 20px;
}
.ubermenu-target.ubermenu-target-with-image {
display: flex;
justify-content: flex-end;
}
}
Hope this clarifies. 🙂