add classnames to canvases

client/src/components/miniHistogram/index.js

@@ -78,6 +78,7 @@ export default class MiniHistogram extends React.PureComponent {
             height,
             borderBottom: "solid rgb(230, 230, 230) 0.25px",
           }}
+          className="mini-histo"
           width={width}
           height={height}
           ref={this.canvasRef}

client/src/components/miniStackedBar/index.js

@@ -63,6 +63,7 @@ export default class MiniStackedBar extends React.PureComponent {
           width,
           height,
         }}
+        className="mini-stacked-bar-canvas"
         width={width}
         height={height}
         ref={this.canvasRef}

client/src/components/scatterplot/scatterplot.js

@@ -502,6 +502,7 @@ class Scatterplot extends React.PureComponent {
             width={width}
             height={height}
             data-testid="scatterplot"
+            className="scatterplot-canvas"
             style={{
               marginLeft: margin.left,
               marginTop: margin.top,