Microsoft Entra Custom Css Login

Question

Hi I'm reading this article about how to customize the visual of login in microsoft entra external ids. I've tried to update the placeholder style of the text boxes using the ::placeholder pseudo-element. When I test the selector directly inside my browser, it works well. When I upload my custom css file, it does not work in production.

.ext-input.ext-text-box::placeholder {
    color: rgb(255, 255, 255, 0.4);
}

I didn't found a selector to update the style of this navigation bar as well. The navigation bar and the back button.