Hover widget shows no text in Safari 10.1

[sandyarmstrong]

monaco-editor version: 0.8.1 (and also whatever's on the official playground)
Browser: Safari 10.1
OS: macOS 10.12.4

Steps to reproduce

1. Open https://microsoft.github.io/monaco-editor/playground.html
2. Hover over any element that should show a hover tooltip.

Expected results

Hover widget tooltip shows.

Actual results

Empty box of the correct size shows, but text is not visible.

Workaround

Click hover widget.

Notes

From what I can tell this worked fine in Safari 10.0, but last week 10.1 was released and broke this.

It is also broken in WebKit apps on macOS 10.12.4 (but I believe works on 10.11 and earlier 10.12 releases).

[sandyarmstrong]

This seems to be some sort of animation regression. I'm now using this workaround:

.monaco-editor .monaco-editor-hover {
    animation: none !important;
}

In the playground, this change only seems to work on the left editor. I guess that has something to do with the iframe'd nature of the other editor?

[rebornix]

It shares the same root cause as #417.