Fix double border in WAT examples

[NiedziolkaMichal]

Problem

Currently yari places grey border around BOB iframe, with exception of JS examples, in which following CSS rule is applied:

.interactive.is-js-height, .interactive.is-shorter-height, .interactive.is-taller-height {
    border: 0;
}

This generally works ok, except for WAT examples, in which double border is applied:

Here is JS for comparison:

Solution

This PR adds grey border to interactive examples, so it can be fully removed from YARI. Examples will look exactly the same way, except for WAT, in which there will be a single border instead of two.

If this gets deployed, temporarily every BOB example except for JS will have 2 borders, because old border will be still applied by YARI. It will be simple CSS change, so it's ok if I make PR in there after deployment of BOB or shortly before it?

This PR depends on #1003, which should be merged first

[github-actions]

This pull request has merge conflicts that must be resolved before it can be merged.