eliminate flickering/flashing while test is running

[willfs84]

There is a flickering/flashing while running Speedometer. It's unpleasant even for people that do not have photosensitive epilepsy and similar issues. There has to be a way to avoid this flashing/flickering (perhaps simply making everything dark mode?)

[bgrins]

It's a good idea to consider. I don't know that there's a way to prevent flickering entirely but there may be some ways to minimize it that don't affect performance.

[willfs84]

It's the high contrast flashing/flickering that's the big problem (white flashing against a black background or vice versa). If they decide to make everything white or everything dark it should pretty much eliminate this

[bgrins]

There's probably more we can do over time, but I'm going to close this out after #151 (making the running iframe always have a light background)