How do I remove blue "selected" outline on buttons?

That is a default behaviour of each browser; your browser seems to be Safari, in Google Chrome it is orange in color!

Use this to remove this effect:

button {
  outline: none; // this one
}

You can remove the blue outline by using outline: none.

However, I would highly recommend styling your focus states too. This is to help users who are visually impaired.

Check out: http://www.w3.org/TR/2008/REC-WCAG20-20081211/#navigation-mechanisms-focus-visible. More reading here: http://outlinenone.com

You can remove this by adding !important to your outline.

button{
 outline: none !important;
}

This is an issue in the Chrome family and has been there forever.

A bug has been raised https://bugs.chromium.org/p/chromium/issues/detail?id=904208

It can be shown here: https://codepen.io/anon/pen/Jedvwj as soon as you add a border to anything button-like (say role="button" has been added to a tag for example) Chrome messes up and sets the focus state when you click with your mouse. You should see that outline only on keyboard tab-press.

I highly recommend using this fix: https://github.com/wicg/focus-visible.

Just do the following

npm install --save focus-visible

Add the script to your html:

<script src="/node_modules/focus-visible/dist/focus-visible.min.js"></script>

or import into your main entry file if using webpack or something similar:

import 'focus-visible/dist/focus-visible.min';

then put this in your css file:

// hide the focus indicator if element receives focus via mouse, but show on keyboard focus (on tab).
.js-focus-visible :focus:not(.focus-visible) {
  outline: none;
}

// Define a strong focus indicator for keyboard focus.
// If you skip this then the browser's default focus indicator will display instead
// ideally use outline property for those users using windows high contrast mode
.js-focus-visible .focus-visible {
  outline: magenta auto 5px;
}

You can just set: