If you quickly wanna test out or prototype layouts, you can add a resize property (+ overflow) and then you can drag the bottom-right corner.
div {
resize: both;
overflow: auto;
}You can also limit it to only horizontal or vertical resizing. Here the Docs. It basically adds inline width and/or height styles on that element.
Browser support: Unfortunately it doesn't work in all browsers. Also, Chrome and Firefox have a different implementation of the min/max. So it kinda limits this to be used only during development or testing.
That demo is way more fun than it should be...... :(