.chart-container {
    position: relative;
    width: 100%;
}

.chart-container::before {
    content: '';
    display: block;
    padding-top: 80%;
}

@media (max-width: 768px) {
    .chart-container::before {
        padding-top: 150%;
    }
}

#mychart {
    position: absolute;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
}