With all the time you spend using Shift, you should be able to customize the look of your personal workspace, right?!
Whether it’s the new, oh-so-clean Light Theme, or the original Dark Theme that you prefer, the choice is yours. If you’re a new Shift customer, you will be asked to choose a theme when you sign in for the first time.
If you’re already using Shift, simply head to Settings > General > Appearance > toggle over to the theme of your choice [Light | Dark]. Shift will automatically update to your chosen theme.