Outlines are mainly used for accessibility parameters and should be preserved for default behavior if you do not provide any mechanism or select focus / accessibility. If you simply delete without providing the same, and the user uses the Keyboard for navigation, he will not be able to find out which link / button he is currently making, and may spoil the overall experience with your page.
Remove the contour from the button
.btn-warning:focus{ outline:0px; }
You can also remove the outline from all buttons using
input[type=button]:focus,input[type=submit]:focus{ outline:0px; }
The default button focus is 1px blue on Chrome. There are many other elements that have outline, you can disable them all using:
*{ outline:0px; }
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