Header widget improvements

[davetapley]

Will you accept a PR to make the icon optional?

textual/src/textual/widgets/_header.py

Lines 153 to 155 in a35e92b

	yield HeaderIcon()
	yield HeaderTitle()
	yield HeaderClock() if self._show_clock else HeaderClockSpace()

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Alternatively perhaps the icon should have some docs to show how to set it. I see ⬇️ but I'm not sure what how you'd change that?

textual/src/textual/widgets/_header.py

Line 27 in a35e92b

icon = Reactive("⭘")

Then it could be allowed to be None (I'd argue that should be the default) and that would be how you turn it off and on?

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Similarly I'm not sure about the default 'click to make it tall' semantics?
It seems like that should be something you should have to opt in to?

e.g. if I have custom content hello there:

But then if someone clicks on it the see the app name below and center aligned? 😬

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Also less critical, but I feel like the default header and footer background colors should be the same?

textual/src/textual/widgets/_header.py

Lines 115 to 119 in a35e92b

	DEFAULT_CSS = """
	Header {
	dock: top;
	width: 100%;
	background: $foreground 5%;

textual/src/textual/widgets/_footer.py

Lines 34 to 36 in a35e92b

	DEFAULT_CSS = """
	Footer {
	background: $accent;

[willmcgugan]

The Header was one of the first widget we did, and it could certainly use some more work.

I think you can set the icon to empty string, or maybe a space to disable it.

[davetapley]

@willmcgugan thanks, would this be the preferred way?

    def on_mount(self) -> None:
        header_icon = self.query_one(HeaderIcon)
        header_icon.icon = ''

[willmcgugan]

Should work. Although I'd probably do it in compose