Adjusting a core Joomla file (i.e., the files that you uploaded before installing Joomla!). Any changes you make to core files will be overwritten during the next update, thus core hack is not recommended. In most cases, there are alternative workaround to change Joomla without hacking the core.
01. Hardware selection
Every slide includes a background, which can be a picture or solid color.
Step 1
To change the background click on the label bar and in the layer window select the style tab.
Step 2
Choose a source from the background top tab then upload an image or pick a background color.