The chart rendered as a PNG image in browser that adds width, height, and min-width properties to the CSS for the image. These CSS properties cause the image to undergo scaling to a slightly smaller size in the browser. The image scaling causes the observed blurriness.
You can resolve the issue but responsive will not work.
To fix the issue.
Set the Chart ToolTip attributes to Chart.
Then use the below css.
img[title$='Chart']
{
height:auto !important;
width:auto !important;
min-width:0 !important;
}