var el = document.querySelector("#answer-25097808 > div > div.answercell.post-layout--right > div.s-prose.js-post-body > pre"); // change yourId to id of your element, or you can write “body” and it will convert all document
var els = el.getElementsByTagName("*");

for(var i = -1, l = els.length; ++i < l;){
    el = els[i]
    s = getComputedStyle(el)
    for (let styleKey in el.style) {
        for (let computedStyleKey in s) {
            let computedStyleKeyCamelCase = computedStyleKey.replace(/\-([a-z])/g, v => v[1].toUpperCase());
            if ((typeof el.style[styleKey] != "function") && (styleKey != 'cssText')){
                if(styleKey == computedStyleKeyCamelCase) {
                    el.style[styleKey] = s[computedStyleKey];
                }
            }
        }
    }
}