react-d3-heatmap/dist/styles/tooltip.css

A customizable calendar heatmap

.react-d3-heatMap-container {
    font-family: Arial, Helvetica, sans-serif;
    animation-name: fadeIn;
    animation-timing-function: ease-in;
}

@keyframes fadeIn {
    0% { opacity: 0 }
    100% { opacity: 1 }
}

@-moz-keyframes fadeIn {
    0% { opacity: 0 }
    100% { opacity: 1 }
}

@-webkit-keyframes fadeIn {
    0% { opacity: 0 }
    100% { opacity: 1 }
}

@-o-keyframes fadeIn {
    0% { opacity: 0 }
    100% { opacity: 1 }
}

.d3-tip {
    line-height: 1;
    padding: 6px;
    background: rgba(0, 0, 0, 0.8);
    color: #fff;
    border-radius: 4px
}

  /* Creates a small triangle extender for the tooltip */
.d3-tip:after {
    box-sizing: border-box;
    display: inline;
    font-size: 10px;
    width: 100%;
    line-height: 1;
    color: rgba(0, 0, 0, 0.8);
    content: "\25BC";
    position: absolute;
    text-align: center;
}

  /* Style northward tooltips specifically */
.d3-tip.n:after {
    margin: -3px 0 0 0;
    top: 100%;
    left: 0;
}