Ok, so a silly mistake was the cause of styles not being applied. I post the solution here because maybe I'm not the only one who makes these little oversights. So... I wasn't importing InputTextModule in the controller

input.component.html

<input type="text" pInputText id="username" />

input.component.ts

@Component({
    selector: 'app-input',
    imports: [InputTextModule],
    templateUrl: './input.component.html',
    styleUrl: './input.component.css'
})