Theme: Revert three theme commits that are causing styling issues (#1983

)

* Revert "Theme: Removes css for ui-state-checked its not used any more"

This reverts commit 1b0e947.

* Revert "Theme: Replace missing definition for default icons"

This reverts commit dde9b83.

* Revert "Theme: Switch icon background to use bgColorContent"

This reverts commit 265b8f5.

This reverts three commits:

* Theme: Removes css for ui-state-checked its not used any more 1b0e947 (#1753)
* Theme: Replace missing definition for default icons dde9b83
* Theme: Switch icon background to use bgColorContent 265b8f5

which caused styling issues when compared to UI 1.12.1.

This unfixes a few issues:

* jquery/download.jqueryui.com#335
* https://bugs.jqueryui.com/ticket/15059
* https://forum.jquery.com/topic/checkboxradio-widget-checkbox-click-doesn-t-work-with-ui-lightness-theme-22-9-2016

However, old & known issues are better than new & unknown ones, especially with our current very limited resources.

Closes gh-1983

themes/base/theme.css

@@ -116,9 +116,10 @@ a.ui-button:active,
 	font-weight: normal/*{fwDefault}*/;
 	color: #ffffff/*{fcActive}*/;
 }
-.ui-icon-background {
-	border: #dddddd/*{borderColorContent}*/;
-	background-color: #ffffff/*{bgColorContent}*/;
+.ui-icon-background,
+.ui-state-active .ui-icon-background {
+	border: #003eff/*{borderColorActive}*/;
+	background-color: #ffffff/*{fcActive}*/;
 }
 .ui-state-active a,
 .ui-state-active a:link,
@@ -136,6 +137,10 @@ a.ui-button:active,
 	background: #fffa90/*{bgColorHighlight}*/ /*{bgImgUrlHighlight}*/ /*{bgHighlightXPos}*/ /*{bgHighlightYPos}*/ /*{bgHighlightRepeat}*/;
 	color: #777620/*{fcHighlight}*/;
 }
+.ui-state-checked {
+	border: 1px solid #dad55e/*{borderColorHighlight}*/;
+	background: #fffa90/*{bgColorHighlight}*/;
+}
 .ui-state-highlight a,
 .ui-widget-content .ui-state-highlight a,
 .ui-widget-header .ui-state-highlight a {
@@ -214,8 +219,7 @@ a.ui-button:active,
 .ui-state-error-text .ui-icon {
 	background-image: url("images/ui-icons_cc0000_256x240.png")/*{iconsError}*/;
 }
-.ui-button .ui-icon,
-.ui-state-default .ui-icon {
+.ui-button .ui-icon {
 	background-image: url("images/ui-icons_777777_256x240.png")/*{iconsDefault}*/;
 }