Try adding the following custom code to the Global Custom CSS Area to reduce the padding inside the mobile search.
.wd-header-search-form-mobile .searchform input[type="text"] {
padding-inline-start: 10px;
padding-inline-end: 37px;
}
Please note that while this custom code will decrease the padding on mobile, some text may still not be fully visible in the search due to the limited horizontal space. For further improvement, it may be necessary to reorganize the header layout.
Kind Regards