tooltip.css

span.tooltip {
    cursor: help;
        /* Will either add a pointer with a question mark or just a question mark */
    position: relative;
        /* Relative to the span elements */
}

.tooltip::before, 
.tooltip::after {
    position: absolute;
    left: 50%;
    display: block;
    opacity: 0;
    z-index: -999;
        /* This ensures that the tooltips are not visible without user interaction */
}

.tooltip:hover::before,
.tooltip:focus::before,
.tooltip:hover::after,
.tooltip:focus::after {
    /* Select bother hover and focus to accomodate users without a keyboard */
    opacity: 1;
    z-index: 999;
}


/* --- Creates a triangle shape with borders ---
        https://css-tricks.com/animation-css-triangles-work/ */
.tooltip::before {
    content: "";
    border-style: solid;
    border-width: 1em 0.75em 0 0.75em;
        /* Creates a triangle with the point facing down */
        /* The thinner the left and right borders the sharper the triangle */
    border-color: rgb(18, 88, 110) transparent transparent transparent;
    bottom: 100%;
        /* Bump it up above the span element */
    margin-left: -0.5em;
        /* Center the arrow, given that it has been moved left 50% */
}

.tooltip:after {
    content: attr(data-tip);
        /* This is where the magic happens. See for more details: 
            http://tympanus.net/codrops/css_reference/attr/ */
    background-color: rgb(18, 88, 110);
    border-radius: 0.25em;
    bottom: 170%;
    width: 13.5em;
    padding: 1em 0.5em;
    margin-left: -6.75em;
        /* margin-left is negative and half the width to center the bubble */
    color: white;
    text-align: center;
    font-size: 0.75em;
}