@webcomponents/webcomponentsjs/src/unresolved.js

Web Components Polyfills

/**
 * @license
 * Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
 * This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
 * The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
 * The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
 * Code distributed by Google as part of the polymer project is also
 * subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 */

'use strict';
// It's desireable to provide a default stylesheet
// that's convenient for styling unresolved elements, but
// it's cumbersome to have to include this manually in every page.
// It would make sense to put inside some HTMLImport but
// the HTMLImports polyfill does not allow loading of stylesheets
// that block rendering. Therefore this injection is tolerated here.
//
// NOTE: position: relative fixes IE's failure to inherit opacity
// when a child is not statically positioned.
let style = document.createElement('style');
style.textContent = ''
    + 'body {'
    + 'transition: opacity ease-in 0.2s;'
    + ' } \n'
    + 'body[unresolved] {'
    + 'opacity: 0; display: block; overflow: hidden; position: relative;'
    + ' } \n'
    ;
let head = document.querySelector('head');
head.insertBefore(style, head.firstChild);