[HAR-100] Added dialog documentation, HTML and CSS

[romypetitjean]

No description provided.

[edgargressie]

The icon and main elements are missing in structure section.

[edgargressie]

The dialog modifiers needs to be directly after the original block.

[edgargressie]

Block modifiers in elements should be placed in the element.

Example

.dialog__icon {
	fill: $color-info-500;

	.dialog--success & {
		fill: $color-success-600;
	}

	...
}

[bartvandebiezen]

@romypetitjean Another small change for the HTML: Dialog and content should be a section, so you can start with an H1 and not be dependent on the parents.