Characters that can break out of an inline style background-image url

<div id="test" style="background-image: url($[chr];width:100%">hello</div>

let myDiv = document.getElementById("test");
function getCSSProperty(element, property) {
            return window.getComputedStyle(element).getPropertyValue(property);
        }
const width = getCSSProperty(myDiv, 'width');
if (width === '100%') {
log(String.fromCharCode($[i]))
  }