ttk, How to position heading inside Labelframe instead of on the border?

This can be done by changing the layout definitions so that the text element is held by the Labelframe layout and the Layoutframe.Label no longer draws the text element. Adding a bit of padding ensures the contained widgets leave the label clear.

Example code:

import sys
import tkinter as tk
import tkinter.ttk as ttk


class CustomLabelframe(ttk.Labelframe):
    def __init__(self, master, **kwargs):
        """Initialize the widget with the custom style."""
        kwargs["style"] = "Custom.Labelframe"
        super(CustomLabelframe, self).__init__(master, **kwargs)

    @staticmethod
    def register(master):
        style = ttk.Style(master)
        layout = CustomLabelframe.modify_layout(style.layout("TLabelframe"), "Custom")
        style.layout('Custom.Labelframe.Label', [
            ('Custom.Label.fill', {'sticky': 'nswe'})])
        style.layout('Custom.Labelframe', [
            ('Custom.Labelframe.border', {'sticky': 'nswe', 'children': [
                ('Custom.Labelframe.text', {'side': 'top'}),
                ('Custom.Labelframe.padding', {'side': 'top', 'expand': True})
            ]})
        ])
        if (style.configure('TLabelframe')):
            style.configure("Custom.Labelframe", **style.configure("TLabelframe"))
        # Add space to the top to prevent child widgets overwriting the label.
        style.configure("Custom.Labelframe", padding=(0,12,0,0))
        style.map("Custom.Labelframe", **style.map("TLabelframe"))
        master.bind("<<ThemeChanged>>", lambda ev: CustomLabelframe.register(ev.widget))
        
    @staticmethod
    def modify_layout(layout, prefix):
        """Copy a style layout and rename the elements with a prefix."""
        result = []
        for item in layout:
            element,desc = item
            if "children" in desc:
                desc["children"] = HistoryCombobox.modify_layout(desc["children"], prefix)
            result.append((f"{prefix}.{element}",desc))
        return result


class App(ttk.Frame):
    """Test application for the custom widget."""
    def __init__(self, master, **kwargs):
        super(App, self).__init__(master, **kwargs)
        self.master.wm_geometry("640x480")
        
        frame = self.create_themesframe()
        frame.pack(side=tk.TOP, fill=tk.BOTH)
        
        for count in range(3):
            frame = CustomLabelframe(self, text=f"Frame {count}", width=160, height=80)
            frame.pack(side=tk.TOP, expand=True, fill=tk.BOTH)
            button = ttk.Button(frame, text="Test")
            button.pack(side=tk.LEFT)
        self.pack(side=tk.TOP, expand=True, fill=tk.BOTH)

    def create_themesframe(self):
        frame = ttk.Frame(self)
        label = ttk.Label(frame, text="Theme: ")
        themes = ttk.Combobox(frame, values=style.theme_names(), state="readonly")
        themes.current(themes.cget("values").index(style.theme_use()))
        themes.bind("<<ComboboxSelected>>", lambda ev: style.theme_use(ev.widget.get()))
        label.pack(side=tk.LEFT)
        themes.pack(side=tk.LEFT)
        return frame


def main(args=None):
    global root, app, style
    root = tk.Tk()
    style = ttk.Style(root)
    CustomLabelframe.register(root)
    app = App(root)
    try:
        import idlelib.pyshell
        sys.argv = [sys.argv[0], "-n"]
        root.bind("<Control-i>", lambda ev: idlelib.pyshell.main())
    except Exception as e:
        print(e)
    root.mainloop()
    return 0

if __name__ == '__main__':
    sys.exit(main(sys.argv[1:]))

It is relatively easy to place ttk.Labelframe text below, on or above the relief graphic. This example uses the text attribute but labelwidget can also be used. In order for the relief to be visible the background color of Labelframe.Label must be set to "".

import tkinter as tk
from tkinter import font
from tkinter import ttk

message = "Hello World"

master = tk.Tk()
style = ttk.Style(master)
style.theme_use(themename = "default")

actualFont = font.Font(
    family = "Courier New", size = 20, weight = "bold")
style.configure(
    "TLabelframe.Label", background = "", font = actualFont)

frame = ttk.LabelFrame(
    master, labelanchor = "n", text = message)
frame.grid(sticky = tk.NSEW)
frame.rowconfigure(0, weight = 1)
frame.columnconfigure(0, weight = 1)

def change_heading():
    if frame["text"][0] == "\n":
        frame["text"] = f"{message}\n"
    else:
        frame["text"] = f"\n{message}"

button = tk.Button(
    frame, text = "Change", command = change_heading)
button.grid(sticky = "nsew")

master.mainloop()

Looking through the source of the Labelframe widget, I found that:

• The label is either placed vertically-centered on the frame's border, or flush above it, depending on the -labeloutside config option. (for default NW anchor)
• i.e. by adding whitespace on top of the text by any means, the label box will extend upwards the same amount as downwards, creating a "dead space" above the frame.
• There might still be a way to get it "inside" by increasing the border width, but I couldn't get it to work.

I now used the labeloutside option to make a "tab-like" heading.

    # ... (define $images array much earlier) ...
    ttk::style element create Labelframe.border image $images(card2) \
        -border 6 -padding 6 -sticky nsew
    ttk::style configure TLabelframe -padding {8 8 8 8} -labeloutside 1 -labelmargins {2 2 2 0}
    ttk::style element create Label.fill image $images(header2) -height 31 -padding {8 0 16 0} -border 1

With suitable images, this is nearly what I was aiming for, only that the header does not stretch across the full frame width. Tkinter elements use a "9-patch"-like subdivision strategy for images, so you can make stretchable frames using the -border argument for element create.

Result is approximately this:

+-------------+
| Heading     |
+-------------+----------------+
| ...                          |