Feature Request: Add secondary themed button

[jfily]

Could you, please, add secondary themed buttons like in https://material-components-web.appspot.com/button.html ?

Thank you

[kfranqueiro]

Buttons are intentionally styled with the primary color by default. We expose Sass mixins to allow easily customizing styles for specific buttons, and the primary and secondary colors are stored in variables initially defined in the mdc-theme package.

Here's the demo SCSS responsible for styling buttons with the secondary-text-button class (with styles for flat, raised/unelevated, and stroked variants):

material-components-web/demos/button.scss

Lines 25 to 38 in 229e590

	.mdc-button.secondary-text-button {
	@include mdc-button-ink-color($mdc-theme-secondary);
	@include mdc-states(secondary);
	}
	.mdc-button.secondary-filled-button {
	@include mdc-button-filled-accessible($mdc-theme-secondary);
	}
	.mdc-button.secondary-stroked-button {
	@include mdc-button-ink-color($mdc-theme-secondary);
	@include mdc-button-stroke-color($mdc-theme-secondary);
	}

If you need to see what these equate to in CSS, the button mixins are defined in https://github.com/material-components/material-components-web/blob/master/packages/mdc-button/_mixins.scss