Placeholder width can't be set to auto #1508
Description
Because of the (convoluted 🤪) way in which I implemented Placeholder, turns out you can't set its width to auto, otherwise the placeholder collapses.
E.g., if you run the app below, you will have an empty screen:
from textual.app import App
from textual.widgets import Placeholder
class MyApp(App):
CSS = """
Placeholder { width: auto; }
"""
def compose(self):
yield Placeholder()