Remove <pre> from nested HTML repr (#4171)

Using `<pre>` messes up the display of nested HTML reprs, e.g., from dask. Now
we only use the `<pre>` tag when displaying text.

xarray/core/formatting_html.py

@@ -20,7 +20,9 @@ def short_data_repr_html(array):
     internal_data = getattr(array, "variable", array)._data
     if hasattr(internal_data, "_repr_html_"):
         return internal_data._repr_html_()
-    return escape(short_data_repr(array))
+    else:
+        text = escape(short_data_repr(array))
+        return f"<pre>{text}</pre>"
 
 
 def format_dims(dims, coord_names):
@@ -123,7 +125,7 @@ def summarize_variable(name, var, is_index=False, dtype=None, preview=None):
         f"<label for='{data_id}' title='Show/Hide data repr'>"
         f"{data_icon}</label>"
         f"<div class='xr-var-attrs'>{attrs_ul}</div>"
-        f"<pre class='xr-var-data'>{data_repr}</pre>"
+        f"<div class='xr-var-data'>{data_repr}</div>"
     )
 
 
@@ -193,7 +195,7 @@ def array_section(obj):
         f"<input id='{data_id}' class='xr-array-in' type='checkbox' {collapsed}>"
         f"<label for='{data_id}' title='Show/hide data repr'>{data_icon}</label>"
         f"<div class='xr-array-preview xr-preview'><span>{preview}</span></div>"
-        f"<pre class='xr-array-data'>{data_repr}</pre>"
+        f"<div class='xr-array-data'>{data_repr}</div>"
         "</div>"
     )
 

xarray/tests/test_formatting_html.py

@@ -48,7 +48,7 @@ def dataset():
 
 def test_short_data_repr_html(dataarray):
     data_repr = fh.short_data_repr_html(dataarray)
-    assert data_repr.startswith("array")
+    assert data_repr.startswith("<pre>array")
 
 
 def test_short_data_repr_html_non_str_keys(dataset):