There are a few options on the market depending on where you are. The specific product I have seems to be out of manufacture now but the replacement is the Samotech Hue Switch cover SM200 V2. It fits over the top of your existing light switch and the wireless dimmer attaches magnetically. If you need to turn off the light completely you can pop the cover and access the switch underneath.

It is a little bit bulky due to the nature of it but that's not something that bothers me. If you're particular about your interior design, you may need to look elsewhere: there are also complete light switch replacement products that are thinner and look a bit sleeker, but I haven't felt the need to move to those.

Another thing I like about the Hue system is I had so much difficulty finding reliable combinations of non-smart dimmer switch and LED light. Despite spending a lot of money to get supposedly high quality LED compatible dimmers, one would break every few months and occasionally they seemed to cause my LED lamps to burn out or have other weird issues like not completely turning off. All dimmer switches I tried had a subtle buzzing at certain light levels too.

It's possible there is some combination of lights and dimmers that works great, but since switching to Hue, it's the first time in my life where my lighting system has required zero maintenance in over a year. Other than when a squirrel bit through my garden string lights...

This: https://www.amazon.com/Lutron-Aurora-Dimmer-Philips-Z3-1BRL-...

You leave the toggle switch in the On position and mount this on top of it. Very clever.

The Hue Dimmer Switch V2 has standard mounting holes on the back plate. You’d need to remove the existing switch.

https://tweakers.net/productreview/292224/philips-hue-dimmer...

If you’re happy with your smart setup it’s trivial to remove the existing switch, connect the wires directly and put a cover on top, then attach the wireless switch to it using adhesive/Velcro.