great links

jQuery | Aspect Ratio Calculator:
https://codepen.io/tobiasdev/pen/XNjxdZ?editors=1010

Responsive Sprite:
https://pagecrafter.com/responsive-background-image-sprites-css-tutorial/

https://css-tricks.com/aspect-ratio-boxes/

https://ratiobuddy.com/

https://www.w3schools.com/howto/howto_css_aspect_ratio.asp

** DOM inspect code base **
https://codemirror.net/

iFrame Demos:
https://www.w3schools.com/howto/howto_css_devices.asp

https://developers.google.com/web/tools/lighthouse/audits/aspect-ratio
https://developers.google.com/web/tools/chrome-devtools/device-mode/

https://css-tricks.com/measuring-image-widths-javascript-carefully/

https://stackoverflow.com/questions/29730535/highlight-non-breaking-spaces-in-html-page-or-wordpress-editor
Whole body: https://jsfiddle.net/y18e0c1w/7/

Show alt+ spacebar: http://jsfiddle.net/Daniel_Hug/qPUEX


https://github.com/chriso/validator.js

Firefox image off issue:
https://stackoverflow.com/questions/486896/adding-a-parameter-to-the-url-with-javascript
https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/setTimeout
https://www.sitepoint.com/jquery-settimeout-function-examples/
https://stackoverflow.com/questions/318630/get-the-real-width-and-height-of-an-image-with-javascript-in-safari-chrome/670433#670433