I used a two-button when I clicked on that button div should be changed using javascript replaced the function the problem is when I click on the button border should be changed by default black color I could not find where it was added that I'm adding screenshots. it happened after I added on click replaced function 
<script>
function replace(hide, show) {
document.getElementById(hide).style.display = "none";
document.getElementById(show).style.display = "block";
}
</script>
<div class="two_btn">
<div class="order_btn">
<button type="button" onclick="replace('div2','div1')">Order & Collect</button>
</div>
<div class="book_collection">
<button type="button" onclick="replace('div1','div2')">Book UK Collection</button>
</div>
</div>
It's an on-focus outline, automatically added by your browser. To remove it completely (not advisable), you can add this to your CSS:
button:focus {
outline: none;
}
Why you should not do this and use a different approach instead:
https://www.a11yproject.com/posts/never-remove-css-outlines/