Improve responsive layout at medium screen widths

At 1200px and below, reduce chart width to 60% and increase details
box width to 38% (min 340px) to prevent amounts from being truncated.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

styles.css

@@ -313,8 +313,13 @@ body {
 
 /* Add responsive design for smaller screens */
 @media (max-width: 1200px) {
+    .chart-wrapper {
+        width: 60%;
+    }
+
     #details-box {
-        max-width: 300px;
+        width: 38%;
+        min-width: 340px;
     }
 }