setActivity(active) {
        const classList = this._element.classList;

        if (active) {
            classList.add('active');
        } else {
            classList.remove('active');
        }
        return this;
    }
Sets the marker's activity state. Active status refers to the state where
the marker is selected and highlighted.
@param {boolean} active - If true, the marker is active
@returns {Marker} Returns itself to allow for method chaining