To use the image uploader, click or press the area above the stats. This will display an uploader sidebar.
Add as many images as you want, separately. Drag them around on the render list to determine depth order.
To change the scale or position of an image, select it from the render list. To move, simply drag on the canvas. To change the scale, click the plus and minus buttons above the render list.
Once you are done with the image uploading and positioning, press close at the bottom to return.
To create a custom theme, change the template option to "Custom". An editor will display which allows you to update the Hue, Saturation, and Value of a primary, secondary, and background color.
To save a custom theme, update the values to your desired theme and press "save theme". This will be saved as a JSON file.
To upload a saved theme, change the template option to "Custom" and press "upload theme". Select your desired JSON file.