The responsive analog clock is something I built a couple years back (see https://front-end-fu.com/2014/04/07/responsive-analog-clock-with-css3-and-javascript/). Recently, I wanted to tweak it so it was responsive relative to its parent element, as opposed to the viewport. To do so, I simply incorporated the CSS-Element-Queries library (http://marcj.github.io/css-element-queries/) to add resize event listeners to page elements. With this, I then bound the resize handler to the section surrounding the clock, rather than the window. Then I made the section resizable by applying the jQuery UI resizable interaction (https://jqueryui.com/resizable/). This allows you to horizontally resize the section by dragging the right border to the left or right, demonstrating that the analog clock is, indeed, responsive to its parent element.