What size image should be to fit under the slider?

Question

css

https://codepen.io/iamdavid/pen/CDluy?page=1
I put the picture 300x400 crooked! What image size do you need?

Answer 1

well, in general, any size of images would not be stretched: https://codepen.io/topicstarter/pen/ddRZeo?editors=1010
I took pictures from gray hair

Answer 2

image in background-image with styles

background-size: cover;
background-position: center;