Strip tertiary headings confusing doc build

docs/example-rain.ipynb

@@ -18,14 +18,14 @@
     "\n",
     "We'll need to tackle two key challenges into visualizing this rainfall time series: *1)* dealing with scrunched time/rainfall scales and *2)* co-visualizing dueling readings from our twin gauges.\n",
     "\n",
-    "### Challenge 1\n",
+    "**Challenge 1**\n",
     "\n",
     "To address the first challenge, we will use `matplotlib`'s `stackplot` to create area plots with a transparency (\"alpha\") effect.\n",
     "(For those unfamiliar, area plots are line plots with the area between the line and the x-axis filled in.)\n",
     "Because the gauges mostly agree, the majority of plotted area will be overlap from both gauges.\n",
     "However, where they differ one area plot will show through.\n",
     "\n",
-    "### Challenge 2\n",
+    "**Challenge 2**\n",
     "\n",
     "The second challenge in visualizing this data arises because, in the particular study area, large amounts of rain falls in short spurts.\n",
     "So, when we zoom out to see the whole month and the maximum rainfall rate, large spikes in the data cause the rest of the data to be scrunched into obscurity.\n",