as you can see in the picture in the same label the standard serif font is "mixed" with my custom font
viewer.entities.add({
                    position: Cesium.Cartesian3.fromDegrees(longitude, latitude),
                    label: {
                      text: result.city,
                      font: '24px Acumin-bold',
                      fillColor: Cesium.Color.WHITE,
                      outlineColor: Cesium.Color.BLACK,
                      outlineWidth: 3,
                      style: Cesium.LabelStyle.FILL_AND_OUTLINE,
                      verticalOrigin: Cesium.VerticalOrigin.BOTTOM,
                      heightReference: Cesium.HeightReference.NONE,
                      pixelOffset: new Cesium.Cartesian2(0, -5),
                      translucencyByDistance: new Cesium.NearFarScalar(minDistance, 1.0,
                        maxDistance, 0.0),
                      disableDepthTestDistance: Number.POSITIVE_INFINITY,
                    }
                  });