Adds window_group_move.css to vivaldi and updates browser.html to use it; meant to be used with https://gist.github.com/szarroug3/2aaf6c129f4da7d288f00d6bb333c21c

customize_vivaldi.py

import os

from shutil import copyfile


def copy_file(dest):
    copyfile('window_group_move.css', dest)


def edit_browser_html(filename):
    with open(filename) as f:
        browser_html = f.readlines()

    head = None
    for i, l in enumerate(browser_html):
        if '</head>' in l:
            head = i
        if 'window_group_move' in l:
            return

    if head:
        browser_html.insert(head, '    <link rel="stylesheet" href="style/window_group_move.css" />\n')
    else:
        raise ValueError('Could not find </head> in browser.html.')

    with open(filename, 'w') as f:
        f.write(''.join(browser_html))


if __name__ == '__main__':
    app_folder = os.path.join(os.path.expanduser('~'), 'AppData', 'Local', 'Vivaldi', 'Application')
    vivaldi_folder = os.path.join(app_folder, os.listdir(app_folder)[0], 'resources', 'vivaldi')

    window_group_move_dest = os.path.join(vivaldi_folder, 'style', 'window_group_move.css')
    copy_file(window_group_move_dest)

    browser_file = os.path.join(vivaldi_folder, 'browser.html')
    edit_browser_html(browser_file)