Cells leave behind output_container elements

[roblourens]

• Execute a cell to get a webview output
• Clear the output
• See that the output_container is still there and taking up space
• Click to focus a markdown cell under this output, nothing happens when I click it because it's covered up by the leftover output

[vscode-triage-bot]

Pinging notebook topic followers: @claudiaregio @rchiodo @greazer @DonJayamanne @jilljac @IanMatthewHuff

[mjbvz]

I'm refactoring this area of the code quite a lot for debt week and will try fixing this

[mjbvz]

I believe this is fixed by dcc6609