Answer 1

list-style-image assumes your image is already resized to the final size. There is really no good way to resize it. use li::before and use the image url as background-image for more control.

li{
list-style: none;
}
li:before{
content:'';
display:inline-block;
height:15px;
width:15px;
background-image:
url(
"https://dl.dropboxusercontent.com/scl/fi/gk46yjjvup8c1k67ibr8y/czNmcy1wcml2YXRlL3Jhd3BpeGVsX2ltYWdlcy93ZWJzaXRlX2NvbnRlbnQvbHIvdjEwMzAtMDUwLXguanBn.jpg?rlkey=s34zqdw1u1ovhe7qjk9jstjzf&dl=0");
background-repeat:no-repeat;
background-size:cover;
margin-right:10px;
}

Answer 2

Wise Wolfie
taking your idea and using canvas as dataURL for ul li bullet image source:

https://sololearn.com/compiler-playground/WJqkqIyDqYsV/?ref=app