Gadget:backToTop.js

// From 萌娘百科

"use strict";
$(function () {
    var btn = insertToBottomRightCorner("返回顶部").attr({
        title: "返回顶部",
        id: "backToTop"
    }).css({
        "user-select": "none",
        transition: "opacity .13s ease-in-out",
        order: "998"
    }).on("click", function () {
        $("html, body").animate({
            scrollTop: 0
        }, 130);
    });
    var $document = $(document);
    $(window).on("scroll", function () {
        btn.css("opacity", $document.scrollTop() > 0 ? ".6" : "0");
    }).trigger("scroll");
});