theme: add heading-style for zt_dark

In order to emphasise the heading tags ranging from h1 to h6, they have been displayed with a different colour. This is to fix issue zulip#1095

Author: mounilKshah

zulipterminal/themes/zt_dark.py

@@ -31,6 +31,7 @@
     'msg_emoji'       : (Color.LIGHT_MAGENTA,       Color.BLACK),
     'reaction'        : (Color.LIGHT_MAGENTA__BOLD, Color.BLACK),
     'reaction_mine'   : (Color.BLACK,               Color.LIGHT_MAGENTA),
+    'msg_heading'     : (Color.LIGHT_CYAN__BOLD,    Color.DARK_MAGENTA),
     'msg_math'        : (Color.LIGHT_GRAY,          Color.DARK_GRAY),
     'msg_mention'     : (Color.LIGHT_RED__BOLD,     Color.BLACK),
     'msg_link'        : (Color.LIGHT_BLUE,          Color.BLACK),

zulipterminal/ui_tools/boxes.py

@@ -1236,6 +1236,9 @@ def soup2markup(
                 text = unrendered_tags[tag]
                 if text:
                     markup.append(unrendered_template.format(text))
+            elif tag in ("h1", "h2", "h3", "h4", "h5", "h6"):
+                # HEADING STYLE (for all heading style tags – h1 to h6)
+                markup.append(("msg_heading", tag_text))
             elif tag in ("p", "del"):
                 # PARAGRAPH, STRIKE-THROUGH
                 markup.extend(cls.soup2markup(element, metadata)[0])