You can do this by Finding the platform they are on then using an if statement to create a stylesheet link
function getOS() {
    var userAgent = window.navigator.userAgent,
      platform = window.navigator.platform
      macosPlatforms = ["Macintosh", "MacIntel", "MacPPC", "Mac68K"],
      windowsPlatforms = ["Win32", "Win64", "Windows", "WinCE"],
      iosPlatforms = ["iPhone", "iPad", "iPod"],
      os = null;
  
    if (macosPlatforms.indexOf(platform) !== -1) {
      os = "Mac OS";
    } else if (iosPlatforms.indexOf(platform) !== -1) {
      os = "iOS";
    } else if (windowsPlatforms.indexOf(platform) !== -1) {
      os = "Windows";
    } else if (/Android/.test(userAgent)) {
      os = "Android";
    } else if (!os && /Linux/.test(platform)) {
      os = "Linux";
    }
  
    return os;
  }
  
  if (getOS() == "Windows") {
    var head = document.getElementsByTagName("HEAD")[0];
    var link = document.createElement("link");
    link.rel = "stylesheet";
    link.type = "text/css";
    link.href = "scrollbar.css";
    head.appendChild(link);
}
note: Where it says scrollbar.css replace it with your CSS file name
Hope this helps.