data-tooltip.css

:root {
  --tooltip-color: snow;
  --tooltip-background: #333;
  --tooltip-border-radius: 3px;
  --tooltip-font-size: 14px;
  --tooltip-padding: 6px 8px;
} 

[data-tooltip] {
  position: relative;

  &:before,
  &:after {
    position: absolute;
    left: 50%;
    
    opacity: 0;
    visibility: hidden;
    z-index: 2;
    
    transition: 0.3s ease;
    transition-property: opacity, transform, visibility;
  }

  &:before {
    content: attr(data-tooltip);
    
    color: var(--tooltip-color);
    background: var(--tooltip-background);
    border-radius: var(--tooltip-border-radius);
    
    line-height: 1.4;
    font-size: 14px;
    font-weight: 600;
    text-align: center;
    letter-spacing: .1;
    
    padding: var(--tooltip-padding);
    box-sizing: border-box;
    min-width: 100px;
    bottom: 100%;
    transform: translate3d(-50%, -7px, 0);
    
    /* optional */
    /* white-space: nowrap; */
  }

  &:after {
    content: '';
    
    border-top: 5px var(--tooltip-background);
    border-left: 3px transparent solid;
    border-right: 3px transparent solid;
    top: 0;
    margin-left: -2px;
    transform: translate3d(0, -7.5px, 0);
  }

  &:focus,
  &:hover {
    &:before,
    &:after {
      opacity: 1;
      visibility: visible;
    }

    &:before {
      transform: translate3d(-50%, -2px, 0);
    }

    &:after {
      transform: translate3d(0, -2.5px, 0);
    }
  }
}