Px2rem

Px2rem is a extension for Brackets.

Setting

The root size is 10px, set root size Ctrl+:.

Using

When the cursor is on the value, press Shift+Tab.

Custom

If you don't like the shortcut, you can reset it. Debug -> Open Your Key Map -> Add your convert key in overrides, such as:

{
    "overrides": {
        "<key>": "me.convert.pxrem"
    }
}

That's my keymap.json:

{
    "overrides": {
	"`": "me.convert.pxrem"
    }
}