Slider Image Custom Height

I am using the Quill theme to create a site ( wanted to customize it a little…the static front page image takes up the whole page. How do I get 100% width coverage but height of the image take up only half the screen?

RqUSAXNKyEt4Whhere do I replace the code in?

you can try to add this code using custom css plugin:

#slides, .overlay {
  height: 340px !important;
#slides img {
  top: 0 !important;

Sorry… I am not super savy. I downloaded custom css plugin and activated it.
Where do i enter this code?

It’s placed under appearance navigation. Appearance > custom css