Check out example codes for "how to remove button decoration". It will help you in understanding the concepts better.

Code Example 1

button {
    border: none;
}

button:focus {
    border: none;
    outline: none;
}

button:focus{
    outline:none !important;
}
(add !important if it is used in Bootstrap)

Code Example 2

button:focus { outline: none; }

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