How to automatically resize image size

Greetings,

I am trying out this plugin. Looks great and works great so far.

The issue we are facing is when an image is added, unless the image is manually resized, it is either bigger or smaller than the rest of the images on List view.

Is there a way to add any image size and have it automatically resized to say 250px by 250px?

I tried these but no luck:

.ecwd-theme-child-free-child p img {
 display: block;
 margin: 0 auto;
 width:  250px !important;
 height: 250px !important;
}
.ecwd_calendar img {
    width: 250px !important;
     height: 250px !important;
}

Again, so far, we are checking out the free version of the calendar.

Thank you very much in advance.