add legend

app.py

@@ -71,6 +71,13 @@ def molecule(input_pdb):
     allow-scripts allow-same-origin allow-popups 
     allow-top-navigation-by-user-activation allow-downloads" allowfullscreen="" 
     allowpaymentrequest="" frameborder="0" srcdoc='{x}'></iframe>
+    <div style="position: absolute; top: 10px; right: 10px; background-color: white; padding: 10px; border: 1px solid black;">
+  <div style="height: 150px; background: linear-gradient(to bottom, red, yellow, green, blue);"></div>
+    <div style="display: flex; justify-content: space-between; margin-top: 5px;">
+        <span>High Energy</span>
+        <span>Low Energy</span>
+    </div>
+    </div>
     <a href="data:application/octet-stream;base64,{base64_content}" download="structure.pdb">Download File</a>
     """