tweak axes, hide y axis on mobile

priv/frontend/src/components/Graph.css

@@ -2,13 +2,21 @@
   width: 100%;
 }
 
+.recharts-cartesian-axis-tick-value {
+  font-size: 0.85em;
+}
+
 .recharts-tooltip-wrapper .recharts-default-tooltip {
-  padding: 0 0.5rem !important;
+  padding: 0 0.5em !important;
   border-radius: 0.2rem;
-  font-size: 0.85rem;
+  font-size: 0.85em;
   opacity: 0.85;
 }
 
+.recharts-default-tooltip li {
+  color: inherit !important;
+}
+
 .recharts-tooltip-item-value {
   font-family: PragmataPro, Menlo, "DejaVu Sans Mono", monospace;
 }

priv/frontend/src/components/Graph.js

@@ -63,10 +63,14 @@ export default class Graph extends Component {
               tickFormatter={(tick) => ms(Date.now() - tick)}
               tickLine={false}
             />
-            <YAxis
-              dataKey="latency"
-              tickLine={false}
-            />
+            {this.isSmallScreen()
+              ? null
+              : <YAxis
+                  dataKey="latency"
+                  tickLine={false}
+                  tickFormatter={(tick) => `${tick}ms`}
+                />
+            }
             <CartesianGrid strokeDasharray="1 1" />
             <Tooltip
               isAnimationActive={false}