#1021 - Dropdowns

[macandcheese]

PR for #1021.

This builds on Julio's work to update the style of dropdown menus - there are no structural changes. Tested in Chrome, FF, Safari, Edge. Waiting for #1070 to test in IE 11.

Changes:

• These should now match Online / discussed updates
• Hit areas for dropdown links are now full width, and have distinct hover / focus states
• Introduces an active-link-dot mixin to use in future designs
• Uses shadow level / strength from Alerts (#1023 - Alerts #1068)
• Uses invocation animation from Online

Questions / Need feedback on:

• Is using content: "\2022" for the pseudo-element active dot sustainable? It makes aligning the active dot with the line-height easy but unsure if there are consequences with translation of the character. Alternatively we can use a bg-color in the pseudo-element.
• I think the current 600 weight items (header, active item) are good candidates for 500 weight treatment.

[julio8a]

• I'm not sure about the sustainability of the pseudo-element, @paulcpederson might have a better idea here.
• Good idea on weight change for titles and active. Worth taking a look once we have 500 in.

[macandcheese]

Updates based on last week's feedback...

• Indent link items, align "active dot" flush left with heading
• remove font-weight adjustment for active state
• small color and padding adjustments

We can use this as the base for filters, side navs, etc