fixed-ui.user.js

// ==UserScript==
// @name         Github fixed ui
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Fix the ui at the top of the page so you can see it when scrolling a long readme
// @author       Josh Parker
// @match        https://github.com/*/*
// @icon         https://www.google.com/s2/favicons?domain=github.com
// @grant        none
// ==/UserScript==

(function fixedUi() {
 const css = `
main#js-pjax-container {
  top: 3rem;
  position: relative;
}
`;
 const style = document.createElement('style');
 style.appendChild(new Text(css));
 document.querySelector('body').appendChild(style);

 const jhwHeader = document.querySelector('div.js-header-wrapper > header');
 jhwHeader.style.setProperty('position', 'fixed');
 jhwHeader.style.setProperty('width', '100%');
 jhwHeader.style.setProperty('height', '4rem');

 const rch = document.querySelector('#repository-container-header');
 rch.style.setProperty('position', 'fixed');
 rch.style.setProperty('background-color', 'white');
 rch.style.setProperty('width', '100%');
 rch.style.setProperty('z-index', '100');
 rch.style.setProperty('top', '4rem');

 const sib = document.querySelector('#repository-container-header + div');
 sib.style.setProperty('position', 'relative');
 sib.style.setProperty('top', '12rem');

 const footer = document.querySelector('footer.footer');
 footer.style.setProperty('position', 'relative');
 footer.style.setProperty('top', '12rem');

 const dls = document.querySelector('div.Layout-sidebar');
 dls.style.setProperty('position', 'fixed');
 dls.style.setProperty('top', '12rem');
 dls.style.setProperty('right', '7rem');
}());