Unit Test: The Alarm set / clear button has a random black border in Chrome browser

[simonjvardy]

Describe the bug
The Alarm set / clear button has a random black border in Chrome browser that isn't evident in other browsers

To Reproduce
Steps to reproduce the behavior:

1. Go to simonjvardy.github.io/world-clock
2. Click on Alam clock accordion
3. Click on the Set Alarm button
4. See error

Expected behavior
The button should have the defined css styling without this additional solid black border

Screenshots
Button clicked:

Mouse clicked elsewhere on the browser window:

Button clicked again:

Desktop (please complete the following information):

• OS: Windows 10
• Browser Chrome
• Version Version 86.0.4240.198 (Official Build) (64-bit)

Additional context
The border disappears if the mouse pointer is clicked anywhere on the screen but reappears if the button is clicked again.
Dev tools seems to indicate that there is a Bootstrap .button css class that may be behind this as this is affecting an HTML <button> element

[simonjvardy]

This happens in Edge as well. Using Dev tools shows no clues so far as the the nature of the black border generated on button click - suspect this is a rendering style of the <button> element in Chrome and Edge that isn't present in Firefox.