I have installed the Sparkling theme on a new blog.
Does the slider automatically cut the featured picture in order to adapt it (so you can have 3 pics the same size in the slider) or do you have to do it manually? I have a post with a normal picture and the slider shows it very small with white space all around it.
Also, can you create a “fixed” slider with three pictures that are not from a post?
Images are not resized for slider and are displayed as is. Slider is not going to upscale, downscale or crop your images. Recommended image size is 1920px by 600px to make it full with on all size monitors.
No this theme does support only featured images from posts. If you need static images you can use some slider plugins such as Meta Slider.