HeatmapWithTime is visualized in the back of overlay image

HeatMapWithTime is visualized in the back of the overlay image, even after including <style>.leaflet-heatmap-layer{z-index:300 !important}</style> in my html.

According to https://github.com/python-visualization/folium/issues/1201, including this <style>.leaflet-heatmap-layer{z-index:300 !important}</style> in my html should bring the Heatmap to the front. However, that did not work.

My map looks like this:

Basemap

m = folium.Map([35, 41], tiles='stamentoner', zoom_start=6)

Land Use Changes

folium.raster_layers.ImageOverlay(
image=dataimage,
bounds=[[ymin, xmin], [ymax, xmax]],
colormap = lambda x: (x, x, x),
name= 'MODIS Transitions 2009 vs. 2017',
opacity=.8,
zindex=1,
overlay=False,
mercator_project=True).add_to(m)

UCDP HeatMap

hm = HeatMapWithTime(data=list(data.values()), # coordinates
index=list(data.keys()), # years
name = 'UCDP events',
radius=10,
auto_play=False,
max_opacity=1).add_to(m)

folium.LayerControl().add_to(m)
m.save('html/index.html')

My html header is attached:
index.txt

Start by reviewing the attached index.txt and reproducing the map using the HeatMapWithTime and ImageOverlay example in the issue. Trace how those layers are rendered and ordered in the saved html, then verify that the heatmap appears in front of the overlay while LayerControl and the existing map setup still work.