Playground areas should be resizable

[lkintact]

Please have a look at how a Playground window looks on my laptop (I run Windows 10 with a display resolution of 3200x1800px, 250% scaled, using Firefox 138.0.1). Because the HTML, CSS, Javascript and result areas aren't resizable, I have to use scrollbars (outlined in red in the linked image) to see the code/result. Since that's rather inconvenient, I suggest that the areas be resizable, at least vertically.