Resolves matplotlib#96.

Not a nice global fix, but by setting the test fixture viewer's theme to
light, napari-matplotlib will give axes dark grey axes, labels, and ticks.

Author: samcunliffe

src/napari_matplotlib/tests/baseline/test_features_scatter_widget_2D.png

@@ -12,6 +12,7 @@
 @pytest.mark.mpl_image_compare
 def test_histogram_2D(make_napari_viewer, astronaut_data):
     viewer = make_napari_viewer()
+    viewer.theme = "light"
     viewer.add_image(astronaut_data[0], **astronaut_data[1])
     fig = HistogramWidget(viewer).figure
     # Need to return a copy, as original figure is too eagerley garbage
@@ -22,6 +23,7 @@ def test_histogram_2D(make_napari_viewer, astronaut_data):
 @pytest.mark.mpl_image_compare
 def test_histogram_3D(make_napari_viewer, brain_data):
     viewer = make_napari_viewer()
+    viewer.theme = "light"
     viewer.add_image(brain_data[0], **brain_data[1])
     fig = HistogramWidget(viewer).figure
     # Need to return a copy, as original figure is too eagerley garbage

src/napari_matplotlib/tests/baseline/test_histogram_2D.png

@@ -11,6 +11,7 @@
 @pytest.mark.mpl_image_compare
 def test_scatter_2D(make_napari_viewer, astronaut_data):
     viewer = make_napari_viewer()
+    viewer.theme = "light"
     widget = ScatterWidget(viewer)
     fig = widget.figure
 
@@ -31,6 +32,7 @@ def test_scatter_2D(make_napari_viewer, astronaut_data):
 @pytest.mark.mpl_image_compare
 def test_features_scatter_widget_2D(make_napari_viewer):
     viewer = make_napari_viewer()
+    viewer.theme = "light"
     widget = FeaturesScatterWidget(viewer)
 
     # make the points data

src/napari_matplotlib/tests/baseline/test_histogram_3D.png

@@ -8,6 +8,7 @@
 @pytest.mark.mpl_image_compare
 def test_slice_3D(make_napari_viewer, brain_data):
     viewer = make_napari_viewer()
+    viewer.theme = "light"
     viewer.add_image(brain_data[0], **brain_data[1])
     fig = SliceWidget(viewer).figure
     # Need to return a copy, as original figure is too eagerley garbage
@@ -18,6 +19,7 @@ def test_slice_3D(make_napari_viewer, brain_data):
 @pytest.mark.mpl_image_compare
 def test_slice_2D(make_napari_viewer, astronaut_data):
     viewer = make_napari_viewer()
+    viewer.theme = "light"
     viewer.add_image(astronaut_data[0], **astronaut_data[1])
     fig = SliceWidget(viewer).figure
     # Need to return a copy, as original figure is too eagerley garbage