Make the `Preview` button sticky in lab editor/creator

[Daksh777]

The problem:
As I keep adding more content to the lab, previewing it becomes difficult because I have to keep scrolling up to preview it and then scroll back down to continue editing

The solution:
Make the Preview button stick to the top

[arpansac]

Thanks again @Daksh777 for citing this! Would you like to take this one up too?