The answer from Crantisz is the best way to do it, I guess. Here's just an addition that might be helpful for the future. I've seen there's another keyframed animation on the Color Ramp in your node tree, the left slider with the black color moves from position 0.0 to 0.99 via keyframes.
Although you might not need a different frame range on that for both objects in this example, just in case you want to control them separately: it would be the best to connect them to the Group Input just like the other value in Crantisz' answer. The problem with a Color Ramp is that you have no inputs for slider positions or colors.
But in a simple case like this where you only have two sliders with greyscale values between 0 and 1 you can easily replace the Color Ramp with a Map Range node:
- the Value input corresponds to the Fac input of the Color Ramp
- From Min is the position of the left slider
- From Max the position of the right slider
- To Min is the greyscale color of the left slider, for example black = 0
- To Max is the greyscale value of the right slider, e.g. white = 1
- and the Result output gives the value corresponding to the ramp's Color output
So you could connect all inputs of the Map Range node to the outside of the GN modifier like Crantisz did with that one value. This way you have external control about the positions and greyscale values as if they were sliders of a Color Ramp.
In your file where you animated the left slider position it would be sufficient to connect the From Min socket to the Group Input node. Then you can duplicate your object and animate that value independently as well.
