cmborchert

This plugin for WordPress adds a background-size controller to the Background Image section in the WordPress Customizer.
You can access the new controller by going to Appearance > Customize from the Dashboard, and clicking on the Background Image section.
Once you’ve added your custom background image, you can set your background-image size to: 
 – “Cover”: As large as possible; fills entire view, with cropping. 
 – “Contain”: As large as possible, without cropping; fits inside of view. 
 – “100% width”: Width fits view perfectly, height may be smaller or larger than view (equivalent to css ‘100% auto’). 
 – “100% height”: Height fits view perfectly, width may be smaller or larger than view (equivalent to css ‘auto 100%’). 
 – “Inherit”: Sets background size to whatever parent element is set to (html, in this case). 
 – “Custom”: Allows you to put in your own css to be applied in the section called “CSS for background-size (if ‘custom’ selected).”
To learn more about the CSS background-size property, go to:
https://developer.mozilla.org/en-US/docs/Web/CSS/background-size 
or 
http://www.w3schools.com/cssref/css3_pr_background-size.asp
<h3>Notes</h3>
Notes: 
*The plugin works by adding styles to the body.custom-background class. If the default custom-background support has been disrupted, then this plugin will not work.

Add Background-Size to Customizer

Allows you to control the background-size of your main background image from the comfort of the customizer, using predetermined values or custom CSS.

dimitris33

This plugin adds suport for the TwentyFifteen theme to the <a href="https://wordpress.org/extend/plugins/styles" rel="ugc">Styles plugin</a>.
About Styles TwentyFifteen
Using this plugin with the Styles plugin you can instantly change the style of the TwentyFifteen theme from the customizer.
Features of the plugin
<ul>
<li>Instant previews</li>
<li>Text size</li>
<li>Google Fonts</li>
<li>Text colors</li>
<li>Border colors</li>
<li>Background colors</li>
<li>Hundreds of options</li>
<li>Consistent interface and names in every theme</li>
<li>Built on WordPress customizer, so Styles grows as WordPress grows</li>
</ul>
Styles and options for all built-in WordPress themes are free. More themes are available at <a href="http://stylesplugin.com" rel="nofollow ugc">StylesPlugin.com</a>.
Free Themes
<ul>
<li>TwentyTen: <a href="http://demo.stylesplugin.com/twentyten" rel="nofollow ugc">Demo</a></li>
<li>TwentyEleven: <a href="http://demo.stylesplugin.com/twentyeleven" rel="nofollow ugc">Demo</a></li>
<li>TwentyTwelve: <a href="http://demo.stylesplugin.com/twentytwelve" rel="nofollow ugc">Demo</a></li>
<li>TwentyThirteen: <a href="http://demo.stylesplugin.com/twentythirteen" rel="nofollow ugc">Demo</a></li>
</ul>
Developer Resources
<ul>
<li><a href="https://github.com/stylesplugin" rel="nofollow ugc">Styles on Github</a></li>
<li><a href="https://github.com/brainstormmedia" rel="nofollow ugc">Brainstorm Media on Github</a></li>
<li>Code Walkthrough: <a href="http://www.youtube.com/playlist?list=PLxj61Fojm1RGevBh10U2qCqjwoH4Awo-P" rel="nofollow ugc">How to add support for your own themes</a></li>
</ul>

Styles: TwentyFifteen

This plugin adds suport for the TwentyFifteen1 theme to the Styles plugin.

Add Background-Size to Customizer vs Styles: TwentyFifteen