How to remove the blue highlight of button on mobile?

I try to remove the blue box that appears on click in front of buttons as you can see below:

Before asking, I have made a lot of research, I have tried the solutions given by the following topics:

• https://stackoverflow.com/questions/3397113/how-to-remove-border-outline-around-text-input-boxes-chrome
• https://stackoverflow.com/questions/22746464/remove-blue-box-around-buttons-html
• https://stackoverflow.com/questions/24222798/how-to-remove-the-blue-box-shadow-border-in-button-if-clicked
• https://stackoverflow.com/questions/20593224/remove-blue-selected-outline-on-buttons/43773106#43773106
• https://stackoverflow.com/questions/20593224/remove-blue-selected-outline-on-buttons
• https://stackoverflow.com/questions/20340138/remove-blue-border-from-css-custom-styled-button-in-chrome
• https://stackoverflow.com/questions/19053181/how-to-remove-focus-around-buttons-on-click

I have tried all the answers! It works on computer but not on mobile.

If you are using a computer, you can try by simulating mobile with the inspector. Here is the button: https://jsfiddle.net/t4ykshst/

#add {
	-webkit-box-sizing: content-box;
	-moz-box-sizing: content-box;
	box-sizing: content-box;
	outline: none;
	cursor: pointer;
	padding: 10px;
	overflow: hidden;
	border: none;
	-webkit-border-radius: 50%;
	border-radius: 50%;
	color: rgba(255, 255, 255, 0.9);
	text-align: center;
	background: #1abc9c;
	-webkit-box-shadow: 0 4px 3px 2px rgba(0, 0, 0, 0.2);
	box-shadow: 0 4px 3px 2px rgba(0, 0, 0, 0.2);
}

#add:active {
	opacity: 0.85;
	-webkit-box-shadow: 2px 2px 2px 0 rgba(0, 0, 0, 0.2);
	box-shadow: 2px 2px 2px 0 rgba(0, 0, 0, 0.2);
}

<input type="button" id="add" value="+" title="" style="position: absolute; left: 0px; top: 0px; width: 52px; height: 52px;" />

You can add:

-webkit-tap-highlight-color: transparent;

You can also add this to your stylesheets to define it globally:

input,
textarea,
button,
select,
a {
  -webkit-tap-highlight-color: rgba(0,0,0,0);
}

Hope this helps :)

You can find the documentation here for more info: https://developer.apple.com/library/archive/documentation/AppleApplications/Reference/SafariWebContent/AdjustingtheTextSize/AdjustingtheTextSize.html#//apple_ref/doc/uid/TP40006510-SW5

* {
    -webkit-tap-highlight-color: transparent;
}

Test it.

There will be no highlighting (at least in Chrome 88+) at all if you remove cursor: pointer from #add selector. And if you need it in the "desktop" mode, use something like this:

@media (min-width: 768px) {
    #add {
        cursor: pointer;
    }
}

You just need to add style="-webkit-tap-highlight-color: transparent;"

-webkit-tap-highlight-color is a non-standard feature (mdn). It won't work in browser like safari 14.

Instead, you can use

{ outline: none; }

or apply it specifically through selector

a:focus,a:visited,a:active{
  outline: none;
}

Try it

add to the button style "cursor: default;"

This will make a cursor:pointer; it turns into a "default", but will remove the blue shadow on the buttons on the mobile screen as you want