How Styling Event List Widget Featured Image with CSS?

Hi

I tried to add a featured image to the event list widget. I found this:

https://theeventscalendar.com/knowledgebase/add-thumbnails-to-upcoming-events-list-widget/

That worked but now the image is displayed as a big ugly square above the text.
I would like to move the featured image to the left and make it smaller.

I did already this steps here:

https://theeventscalendar.com/knowledgebase/styling-events-widgets/#dl_core-list-widget

But the problem is I have no idea about CSS so please could someone help me with this?

Thanks a lot!

https://wordpress.org/plugins/the-events-calendar/