Vertical alignment of radio/checkbox broken

Created by: drauch

Bug reports must include:

• Operating system and version: Windows 10
• Browser and version: Chrome 70
• Reduced testcase: https://getbootstrap.com/docs/4.0/components/forms/#default-stacked

Even in the default theme it is visible that the radio/checkbox controls are slightly located upwards compared to the label text. It becomes more apparent if you use a custom theme.