replace the arrow

Hi,
I want to replace the down arrow image and I have followed the instructions in the Advanced Use Cases of the documentation. Below is what this says (below ====).

I have copied the image as described and added the css, but the image just disappears when I do this.

Please help. Thx.

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To make update-proof modifications to the arrows, place the new arrow images in the same folder as the child-theme style.css file. Then, add the following to the style.css file or the theme quick-css section:

CSS:
.collapseomatic {
background-image: url(your_down_arrow_image_here.png) !important;

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