Book details panel: De-emphasize titles making the actual data stand out more. Fixes #2029723 [[Enhancement] Suggestions to make the Book details panel look nicer](https://bugs.launchpad.net/calibre/+bug/2029723)

src/calibre/ebooks/metadata/book/render.py

@@ -93,7 +93,7 @@ def mi_to_html(
         mi,
         field_list=None, default_author_link=None, use_roman_numbers=True,
         rating_font='Liberation Serif', rtl=False, comments_heading_pos='hide',
-        for_qt=False, vertical_fields=(), show_links=True,
+        for_qt=False, vertical_fields=(), show_links=True, gray='#7f7f7f',
     ):
 
     link_markup =  '↗️'
@@ -147,7 +147,8 @@ def mi_to_html(
         name = metadata['name']
         if not name:
             name = field
-        name += ':'
+        sep = '\xa0'
+        name += sep
         disp = metadata['display']
         if (metadata['datatype'] == 'comments' or field == 'comments'
             or disp.get('composite_show_in_comments', '')):
@@ -224,7 +225,7 @@ def mi_to_html(
                                     num_of_folders = 2
                                     break
                         text = _('Book files')
-                        name = ngettext('Folder:', 'Folders:', num_of_folders)
+                        name = ngettext('Folder', 'Folders', num_of_folders) + sep
                     links = ['<a href="{}" title="{}">{}</a>{}'.format(action(scheme, book_id=book_id, loc=loc),
                         prepare_string_for_xml(path, True), text, extra)]
                     if num_of_folders > 1:
@@ -425,7 +426,11 @@ def mi_to_html(
         classname(fieldl), html) for fieldl, html in ans]
     # print '\n'.join(ans)
     direction = 'rtl' if rtl else 'ltr'
-    rans = '<style>table.fields td { vertical-align:top}</style><table class="fields" style="direction: %s; ' % direction
+    rans = (
+        '<style>table.fields td { vertical-align:top} table.fields td.title {'
+        f'text-align: right; color: {gray}; font-style: italic; font-weight: normal '
+        '}</style>'
+        '<table class="fields" style="direction: %s; ' % direction)
     if not for_qt:
         # This causes wasted space at the edge of the table in Qt's rich text
         # engine, see https://bugs.launchpad.net/calibre/+bug/1881488

src/calibre/gui2/book_details.py

@@ -8,7 +8,7 @@ from collections import namedtuple
 from contextlib import suppress
 from functools import lru_cache, partial
 from qt.core import (
-    QAction, QApplication, QClipboard, QColor, QDialog, QEasingCurve, QIcon,
+    QAction, QApplication, QClipboard, QColor, QDialog, QEasingCurve, QIcon, QPalette,
     QKeySequence, QMenu, QMimeData, QPainter, QPen, QPixmap, QPropertyAnimation, QRect,
     QSize, QSizePolicy, QSplitter, Qt, QTimer, QUrl, QWidget, pyqtProperty, pyqtSignal,
 )
@@ -292,11 +292,15 @@ def render_data(mi, use_roman_numbers=True, all_fields=False, pref_name='book_di
     field_list = get_field_list(getattr(mi, 'field_metadata', field_metadata),
                                 pref_name=pref_name, mi=mi)
     field_list = [(x, all_fields or display) for x, display in field_list]
+    gray = '#888'
+    app = QApplication.instance()
+    if app is not None and app.is_dark_theme:
+        gray = app.palette().color(QPalette.ColorRole.PlaceholderText).name()
     return mi_to_html(
         mi, field_list=field_list, use_roman_numbers=use_roman_numbers, rtl=is_rtl(),
         rating_font=rating_font(), default_author_link=default_author_link(),
         comments_heading_pos=gprefs['book_details_comments_heading_pos'], for_qt=True,
-        vertical_fields=vertical_fields, show_links=show_links
+        vertical_fields=vertical_fields, show_links=show_links, gray=gray
     )
 
 # }}}