[demo] Split code and diffs into 2 separate columns to avoid overflow

[TomasVotruba]

Current solution uses position: absolute that disallows clearing div. That's why code overflows to next element.

The only path nows seems spliiting into 2 columns: one with origin code and 2nd with diffs.

Closes #2957

[samsonasik]

It seems on default example, it cause splitted right bottom

[TomasVotruba]

@samsonasik I'll check it, thanks for testing 👍

[TomasVotruba]

It seems it's a dead end - either we break diff positions, or the diff overflows to text.

I came up with a creative solution, to tidy up buttons under text - there should be 1 button a page anyway 🤗

It looks pretty cool: there is section on the left with all details and actions, and right is space for diffs.

↓

Before 🧓

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After :party:

[samsonasik]

It seems "Add a test fixture" link is not shown on default example

[samsonasik]

Oh I see, create a fixture only doable on 1 rule applied.