Use JavaScript to calculate width of each list, add them to an array, select max value and assign it to each list. The following code is tested and works great:
var lists = document.querySelectorAll(".progress li");
var arrayList = [];
for (var i = 0; i < lists.length; i++) {
var eachList = lists[i].offsetWidth;
arrayList.push(eachList);
var MaxWidth = Math.max.apply(null, arrayList);
lists[i].style.width = MaxWidth +"px";
}
Here is a jsFiddle:
https://jsfiddle.net/rowin_aria/2szow6rb/2/
its not css, however few lines of JS will save you scratching your head plus this gives you an accurate result