problem with responsive in the Slider

I’m using the Sydney theme, which is great.
But I have a problem, replace the text of the slider with a picture but on cell phones when you see it in a vertical form, the background is very small and the image is huge.
On the other hand, horizontally, the image and the background look good.

How can i fix this ?

My site is

I hope your answers

Hello there,

It looks like you’ve already accomplish it by using a PNG image with huge empty spaces surrounding the logo. Is that correct?