Full code sample for my Medium article: You Should Style the Wrong Button State

pulse-effect-full-code.css

button {
    position: relative;
    margin: 2em;
    padding: 1em 2em;

    background-color: hsl(0, 0%, 100%);
    border: none;
    border-radius: 5px;
    box-shadow: 0 0 0 0px hsla(220, 80%, 70%, 1), 0 4px 5px 1px hsla(0, 0%, 10%, 0.1);

    color: hsl(0, 0%, 10%);
    font-weight: bold;
    letter-spacing: 2px;

    transition: box-shadow 100ms ease-out, background-color 100ms ease-out;
}

/* USUAL FEEDBACK */

button:hover, button:focus, button:active {
    outline: none;
}

button:hover {
    cursor: pointer;
    background-color: hsl(220, 80%, 97%);
}
button:active {
    background-color: hsl(220, 80%, 94%);
}

button:focus, button:active {
    box-shadow: 0 0 0 4px hsla(220, 80%, 70%, 1), 0 4px 5px 1px hsla(0, 0%, 10%, 0.1);
}

/* PULSE EFFECT */

button::before {
    content: " ";
    position: absolute;
    top: 1px;
    bottom: 1px;
    left: 1px;
    right: 1px;

    border-radius: 10px;
    background-color: hsla(230, 80%, 80%, 1);
    opacity: 1;

    z-index: -1;
    pointer-events: none;
}

button:not(:active)::before {
    transition: all 0.3s ease-out, opacity 0.2s 0.1s ease-out;

    top: -20px;
    bottom: -20px;
    left: -20px;
    right: -20px;

    opacity: 0;
}