Custom share js + css

css.css

/* Parts taken from SPCSS 
License: Copyright (c) 2020-2021 Susam Pal
https://github.com/susam/spcss/blob/master/LICENSE.md
*/
#menu {
    border-right: 8px dashed;
    border-radius: 10px;
    border-image: linear-gradient(45deg, red, blue) 1;
    width: 10px;
    margin-right: 25px;
    padding-right: 40px;
}
#layout {
    max-width: 1800px;
}
#noteClippedFrom {
    color: #8f9768;
}
#parentLink {
    font-weight: bold;
    font-size: 18px;
    color: #66afe3;
    border: 4px solid;
    border-radius: 10px;
    padding-left: 4px;
    padding-right: 4px;
    padding-top: 2px;
    padding-bottom: 2px;
    margin-bottom: 15px;
}
#main {
    color: #d0cccc;
}
#buttons {
    height: 30px;
    padding: 10px 0 10px 0;
    margin: 20px 0 20px 0;
    color: #666;
    border: 1px solid #ddd;
    border-left: 0;
    border-right: 0;
}
a:visited {
    color: #1e00ed;
}
body {
    background: #111;
    color: #bbb;
    font-family: helvetica, arial, sans-serif;
    line-height: 1.5;
    margin: 0 auto;
    max-width: 80em;
    padding: 0 1em;
}
h1,
h2,
h3,
h4,
h5,
h6 {
    margin: 1.25em 0 0.5em 0;
    line-height: 1.2;
}
a:link {
    color: #009ded;
}
a:focus,
a:hover {
    color: #03f;
}
a:active {
    color: #e00;
}
h1 a:empty:before,
h2 a:empty:before,
h3 a:empty:before,
h4 a:empty:before,
h5 a:empty:before,
h6 a:empty:before {
    content: "#";
}
h1 a:empty,
h2 a:empty,
h3 a:empty,
h4 a:empty,
h5 a:empty,
h6 a:empty {
    visibility: hidden;
    padding-left: 0.25em;
}
h1:hover a:empty,
h2:hover a:empty,
h3:hover a:empty,
h4:hover a:empty,
h5:hover a:empty,
h6:hover a:empty {
    visibility: visible;
}
img {
    max-width: 100%;
}
figure {
    margin: 1em 0;
    text-align: center;
}
figcaption {
    font-size: small;
}
pre,
code,
samp,
kbd {
    color: #71d22e;
    font-family: monospace, monospace;
}
pre kbd {
    color: #060;
}

blockquote {
    background: #8d83ae6e;
    padding: 0.5em;
}
pre {
    padding: 0.5em;
    background: #0000006e;
}

pre {
    overflow: auto;
}
blockquote {
    border-left: medium solid #ccc;
    margin: 1em 0;
}
blockquote :first-child {
    margin-top: 0;
}
blockquote :last-child {
    margin-bottom: 0;
}
table {
    border-collapse: collapse;
}
th,
td {
    border: thin solid #999;
    padding: 0.3em 0.4em;
    text-align: left;
}

/* Toast bar */
#snackbar {
  visibility: hidden;
  min-width: 250px;
  margin-left: -125px;
  background-color: #333;
  color: #fff;
  text-align: center;
  border-radius: 2px;
  padding: 16px;
  position: fixed;
  z-index: 1;
  left: 50%;
  bottom: 30px;
}

#snackbar.show {
  visibility: visible;
  -webkit-animation: fadein 0.5s, fadeout 0.5s 2.5s;
  animation: fadein 0.5s, fadeout 0.5s 2.5s;
}

@-webkit-keyframes fadein {
  from {bottom: 0; opacity: 0;}
  to {bottom: 30px; opacity: 1;}
}

@keyframes fadein {
  from {bottom: 0; opacity: 0;}
  to {bottom: 30px; opacity: 1;}
}

@-webkit-keyframes fadeout {
  from {bottom: 30px; opacity: 1;}
  to {bottom: 0; opacity: 0;}
}

@keyframes fadeout {
  from {bottom: 30px; opacity: 1;}
  to {bottom: 0; opacity: 0;}
} 
/* Toast bar */

/* Highlight on anchor */
:target {
   background: #68684d;
}

javascript.js

var script = document.createElement("script");
script.src = "https://cdn.jsdelivr.net/npm/anchor-js/anchor.min.js";
script.type = "text/javascript";

script.onload = function () {
    anchors.options = {
        //        visible: "always",
        icon: "",
    };
    anchors.add();
    anchors.add("#content li"); // Every element in content that is part of a list. Now you can link to a specific bullet point
};

document.getElementsByTagName("head")[0].appendChild(script);

document.body.onkeyup = function (e) {
    if (e.keyCode == 37) {
        if (prev === undefined) {
            toast("No previous note!");
        } else {
            if (!loading) {
                window.location.href = prev;
                loading = true;
            }
        }
    }
    if (e.keyCode == 39) {
        if (next === undefined) {
            toast("No next note!");
        } else {
            if (!loading) {
                window.location.href = next;
                loading = true;
            }
        }
    }
};

function toast(text) {
    var x = document.getElementById("snackbar");
    x.className = "show";
    x.innerText = text;
    setTimeout(function () {
        x.className = x.className.replace("show", "");
    }, 3000);
}

if (document.getElementById("menu") !== undefined && document.getElementById("menu").getElementsByTagName("li") !== undefined)  {
    var x = document.getElementById("menu").getElementsByTagName("li");
    var num = 0;
    var prev;
    var next;
    var loading; // stops a mildly annoying glitch when repeatedly clicking arrow
    for (let i = 0; i <= x.length - 1; i++) {
        if (x[i].children[0].innerHTML.includes("strong")) {
            num = i;
            break; //Break loop, always chooses first note in the case of cloned note.
        }
    }
    var y = document.getElementById("main");
    y.innerHTML += '<div id="snackbar"></div>';
    if (x[num - 1] === undefined) {
        var first = '<a class="disabled" style="float:left;">&lt; Previous</a>'; // There's no previous notes, so no link
    } else {
        var first = '<a style="float:left;" href="' + x[num - 1].children[0].children[0].href + '">&lt; Previous</a>';
        prev = x[num - 1].children[0].children[0].href;
        // Previous note exists, so set link to the href value of it
    }
    if (x[num + 1] === undefined || x[num + 1].children[0].children[0].href === undefined) {
        var second = '<a class="disabled" style="float:right;">&gt; Next</a>'; // No next note, so no link
    } else {
        var second = '<a style="float:right;" href="' + x[num + 1].children[0].children[0].href + '">&gt; Next</a>';
        next = x[num + 1].children[0].children[0].href;
        // Next note exists, so set link to the href value of it.
    }
    y.innerHTML += '<br><br><div id="buttons">' + first + second + "</div>";
}