Fitting image correctly in header

Trying to fit an image as a header using the free version of the Hestia theme. This image will be used for all pages as a header.

Link to website: https://stichtingieaf.nl/u-kunt-ook-helpen/
Link to image: https://stichtingieaf.nl/wp-content/uploads/2021/11/Header_final.jpg

Image size: 1637 x 300 pixels

According to my limited knowledge of css/html, I inspected the header and found that it the entire header (including menu, was 1988 x 420 pixels.

Tried resizing the height to 250 px, 225, 200 and even 175 but it never really fits well!

This is the css code I used to increase the height of the header:

.page-header.header-small {
	height: 400px !important;
}

Acoording to hestia documentation, you can use this code to increase the header

.page-header .container {
    height: 600px !important;
    padding-top: 320px !important;
}

However, this code (and changing the values) doesn’t do anything for my page.

Hoping someone here can help me out!

The page I need help with: [log in to see the link]