Image Switch

I've added a hover provision to the circle which takes the opacity down to 0.
If I just had another image there whose opacity could go up at the same time...

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 Getting clear on what trumps what. The last moon, with
both id and class active shows the id settings...

to be absolutely sure: with a 2px blur on id, but a 10px blur on class.

With invert: the original is inverted 10%, as is class. Id carries invert at 20%.

There are, however, considerations in use: an id tag can only apply to
one object in a program, whereas class can apply to many!

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 For those concerned with the effects of a blur filter, below
we have a vector image I made in Expression Blend, and exported as a
png.
With a blur filter at 5px, it blurs;
With a blur filter at -5px, nothing happens;
With a blur filter at 5px, and a blur filter at -5px, the image reverts to normal;
Using an already blurred image I made in Blend, a -5px filter does nothing.