Add id to stylesheet element (#84)

Dynamically add id to the stylesheet element.

This will add an id like `bulma-css` for default theme, 
and `bulma-css-<theme_name>` for any other theme.

Author: GDWR

django_simple_bulma/templatetags/django_simple_bulma.py

@@ -28,9 +28,11 @@ def bulma(theme: str = "") -> SafeString:
 
     # Build the html to include the stylesheet
     css = static(f"css/{theme + '_' if theme else ''}bulma.css")
+    stylesheet_id = f"bulma-css-{theme}" if theme else "bulma-css"
+
     html = [
         f'<link rel="preload" href="{css}" as="style">',
-        f'<link rel="stylesheet" href="{css}">',
+        f'<link rel="stylesheet" href="{css}" id="{stylesheet_id}">',
     ]
 
     # Build html to include all the js files required.