<rh-tile> should default to setting a background of lightest

[zeroedin]

Initial report:

Michael Wells [Oct 18th at 11:17 AM]
new thing. rh-tile used to have a white bg as a default, it no longer does. is that purposeful?

Excerpt from rh-tile.css

https://github.com/RedHat-UX/red-hat-design-system/blob/33f88dab8e4a3f9e329c2fd3614e3363a3e00fc8/elements/rh-tile/rh-tile.css#L60-L65

Tile currently is only setting its background color when explicitly given a palette. Otherwise it allows the background of whatever its placed on to bleed through (this could be bad for accessibility)

Question:
With the implementation of theming tokens, should tile set it's color-palette="lightest" if left undefined.

Excerpt from rh-tile.ts

red-hat-design-system/elements/rh-tile/rh-tile.ts

Lines 127 to 136 in 33f88da

	/**
	* Sets color palette, which affects the element's styles as well as descendants' color theme.
	* Overrides parent color context.
	* Your theme will influence these colors so check there first if you are seeing inconsistencies.
	* See [CSS Custom Properties](#css-custom-properties) for default values
	*
	* Tile always resets its context to `base`, unless explicitly provided with a `color-palette`.
	*/
	@colorContextProvider()
	@property({ reflect: true, attribute: 'color-palette' }) colorPalette?: ColorPalette;

The comment, gives me pause. Base was a concept we haven't implemented. I'm assuming the code here was written to still fulfill this orphaned idea?

Tile always resets its context to base, unless explicitly provided with a color-palette.

Should the fix be. If color-palette is undefined set to lightest

  @colorContextProvider()
  @property({ reflect: true, attribute: 'color-palette' }) colorPalette: ColorPalette = lightest;

or in the css when .light or .dark gets set to the #outer

  &.light {
    --rh-color-surface: var(--rh-color-surface-lightest, #ffffff);
  &.dark {
    --rh-color-surface: var(--rh-color-surface-darkest, #151515);
    --_focus-background-color:
      var(--rh-tile-focus-background-color,
        var(--rh-color-surface-darker, #1f1f1f));
    --_disabled-background-color:
      var(--rh-tile-disabled-background-color,
        var(--rh-color-surface-dark, #383838));
  }

and move that above the & .palette-lightest - darkest rules?

Doing the later will cause a tile to always appear "darkest" on a dark parent context, unless overridden by setting its own color-palette.