[DOC] Properly render sp_list description (#5932)

sktime/transformations/series/fourier.py

@@ -45,12 +45,16 @@ class FourierFeatures(BaseTransformer):
     ----------
     sp_list : List[float and/or str]
         List of seasonal periods. Can be defined with the following options:
+
         * float : Periodicity defined as number of timesteps since the beginning of the
-        data seen in `fit`.
+            data seen in ``fit``.
+
         * string : Periodicity defined as a column name in X that contains the
-        :math:`t/sp` values
+            :math:`t/sp` values.
+
         * string : Periodicity defined as a pandas period alias:
         https://pandas.pydata.org/pandas-docs/stable/user_guide/timeseries.html#period-aliases
+
     fourier_terms_list : List[int]
         List of number of fourier terms (:math:`K`) per corresponding (:math:`sp`); each
         :math:`K` matches to one :math:`sp` of the sp_list. For example, if sp_list =
@@ -63,7 +67,7 @@ class FourierFeatures(BaseTransformer):
         match a pandas offset alias:
         https://pandas.pydata.org/pandas-docs/stable/user_guide/timeseries.html#offset-aliases
     keep_original_columns : boolean, optional, default=False
-        Keep original columns in X passed to `.transform()`
+        Keep original columns in X passed to ``.transform()``
 
     References
     ----------