discourse/app/assets/stylesheets/mobile/select-kit/select-kit.scss

.select-kit {
  &.is-expanded {
    z-index: z("dropdown");
  }

  .select-kit-body {
    width: 100vw;
  }

  .select-kit-filter {
    .filter-input {
      font-size: 16px;
    }
  }
}