Label styling in Micello SDK for leaflet is different from the Micello v0 SDK. We changed the property "t" (text) to "l" (label).

Label property exist at two levels in theme override object now, first inside the object type (Unit, Background, Roon etc.), which defines the style of a label you want to apply.

"s": {
    "Unit": {
        "m": "#cec1a5",
        "o": "#b2a177",
        "l": "Modern",     // label style
        "w": 2
    }
}

Now you can define all the label styles in a separate object.

"l": {
    "Modern":{"fill": "#ffffff"}
}

Full theme override object will look like this:

{
    "s": {
        "Unit": {
            "m": "#cec1a5",
            "o": "#b2a177",
            "l": "Modern",
            "w": 2
        }
    },
    "l": {
        "Modern":{"fill": "#ffffff"}
    }
};

Micello SDK for leaflet allows you multiple options to style your label. Full list of available options are available here.