Renamed the dark theme previewer demo

DemoPrograms/Demo_Theme_Previewer_Dark.py

@@ -0,0 +1,47 @@
+import PySimpleGUI as sg
+# import PySimpleGUIWeb as sg
+# import PySimpleGUIQt as sg
+
+"""
+    If you're using the PySimpleGUI color themes, then your code will a line that looks something like this:
+        sg.theme('Light Green 1') or sg.theme('LightGreen1')
+        
+    This demo shows how to access the list of all "dark themes" as an example of how you can build your own previewer
+    
+    Copyright 2020 PySimpleGUI.org
+"""
+
+# Use the built-in Theme Viewer to show all of the themes and their names
+# sg.theme_previewer()
+
+# The remainder of the program duplicates the built-in Theme Viewer, allowing you to create your
+# own custom theme viewer window.  You can configure the number of frames per row for example. Or maybe you only
+# want to see the dark themes
+
+window_background = 'black'
+
+def sample_layout():
+    """
+    Creates a small window that will represent the colors of the theme. This is an individual theme's preview
+    :return: layout of a little preview window
+    :rtype: List[List[Element]]
+    """
+    return [[sg.Text('Text element'), sg.InputText('Input data here', size=(15, 1))],
+            [sg.Button('Ok'), sg.Button('Cancel'), sg.Slider((1, 10), orientation='h', size=(10, 15))]]
+
+
+layout = [[sg.Text('List of Dark Themes Provided by PySimpleGUI', font='Default 18', background_color=window_background)]]
+
+FRAMES_PER_ROW = 9
+names = [name for name in sg.theme_list()  if 'dark' in name.lower()]       # get list of only "dark" themes
+row = []
+for count, theme in enumerate(names):
+    sg.theme(theme)
+    if not count % FRAMES_PER_ROW:
+        layout += [row]
+        row = []
+    row += [sg.Frame(theme, sample_layout())]
+if row:
+    layout += [row]
+
+sg.Window('Custom Preview of Themes', layout, background_color=window_background).read(close=True)