Twenty Seventeen: Improve display of video header and header image in modern browsers

The theme uses a hack to help the video header and header image fill the available space. This centers around `max-width: 1000%;`. It causes visual issues (zooming of the header video or image) for all users though.

This fixes that with CSS Features Queries. The hack remains for browsers that don't support Feature Queries  and `object-fit`. Browsers that do support both get a better experience with a more reliable styling of the video and image header container.

Props laurelfulford, peterwilsoncc.

Fixes #39035.

Built from https://develop.svn.wordpress.org/trunk@39483


git-svn-id: http://core.svn.wordpress.org/trunk@39423 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-content/themes/twentyseventeen/style.css

@@ -1690,6 +1690,24 @@ body:not(.title-tagline-hidden) .site-branding-text {
 	transform: translateX(-50%) translateY(-50%);
 }
 
+/* For browsers that support 'object-fit' */
+@supports ( object-fit: cover ) {
+	.has-header-image .custom-header-media img,
+	.has-header-video .custom-header-media video,
+	.has-header-video .custom-header-media iframe {
+		height: 100%;
+		left: 0;
+		-o-object-fit: cover;
+		object-fit: cover;
+		top: 0;
+		-ms-transform: none;
+		-moz-transform: none;
+		-webkit-transform: none;
+		transform: none;
+		width: 100%;
+	}
+}
+
 .wp-custom-header .wp-custom-header-video-button { /* Specificity prevents .color-dark button overrides */
 	background-color: rgba(34, 34, 34, 0.5);
 	border: 1px solid rgba(255, 255, 255, 0.6);

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.8-alpha-39482';
+$wp_version = '4.8-alpha-39483';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.