what have you tried?
tried this to change icon size
What ui element are you using?
Can you provide your flow?
there is only ui_Switch and network nodes(mqtt in/out)
I'm not sure if you can change the icon size in the
ui-switch. You could try building your on switch in a template node.
Maybe us fa icons instead - much easier to control the size eg
(full names are fa-toggle-on and fa-toggle off)