<!DOCTYPE html>
<style>
button {
    border: 0;
    padding: 0;
    background-color: white;
    font-family: sans-serif;
    font-size: initial;
    width: 300px;
    display: flex;
    justify-content: center;
}
</style>
<h4>Test for centering text inside a button set to display flex and justify-content: center is impossible</h4>
<button>text with justify-content: center</button>