custom properties defined in :host don't reapply if the rule is inside a media query.

[blasten]

Description

Say you have:

:host {
  display: block;
  --color: red;
}

div {
  color: var(--color);  
}

@media (max-width: 800px) {
  :host {
    --color: blue;
  }
}

Live Demo

https://jsbin.com/mekike/edit?html,output

Expected Results

I'd expect the div's color to be blue if the media query is matching.

Actual Results

The div's color remains red unless you refresh the browser.

Browsers Affected

• All browsers

Versions

• Polymer: master and useNativeCSSProperties = false

[dfreedm]

This is due to the style caching system thinking :root and :host properties do not need to be rechecked on updateStyles().
The simple fix is to disable style caching, and the harder fix is to only disable style caching when @media or :host() selectors are used

[dfreedm]

@sorvell