While in Sciter, that has such immediate mode rendering form the very beginning, you can simply draw them as:
resizableElement.paintForeground = function(gfx) { // draw on top of background & content
let box = this.getBoundingClientRect();
gfx.moveTo(...); gfx.lineTo(...);
gfx.moveTo(...); gfx.lineTo(...);
...
}
Easy, right? And does not need to modify DOM and place artificial positioned elements.