Add header

Author: eric496

0. Data Types.ipynb

@@ -353,7 +353,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "```astype``` method: convert an array to another data type. \n",
+    "### Type Conversion"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "```astype``` method: convert the data type of an array to other data types. \n",
     "\n",
     "Notice that ```astype``` returns a copy of the array instead of converting the data type in place. You need to assign the copy to the original array or a new array."
    ]
@@ -384,7 +391,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "<font color=red>__WARNING__</font>: be cautious about data overflow when you downcast the data type (from higher precision to lower precision). Some unexpected and undefined values might occur and it is usually difficult to debug such issues. "
+    "__WARNING__: be cautious about data overflow when you downcast the data type (from higher precision to lower precision). Some unexpected and undefined values might occur and it is usually difficult to debug such issues. "
    ]
   },
   {