Replace empty placeholder image with empty `<div>`

visualizer/static/style.css

@@ -208,19 +208,28 @@ select:disabled {
 
 #visualization {
   margin-top: 8px;
+  width: 100%;
+}
+
+#plot {
+  width: 100%;
 }
 
-#plot img {
+#plot > img,
+#plot > div {
   aspect-ratio: 1200 / 600;
   background: white;
   background-image: url('data:image/svg+xml;base64,PHN2ZyB2ZXJzaW9uPSIxLjEiIHZpZXdCb3g9IjAgMCAzODQgMTkyIiB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciPgogPHJlY3QgeD0iMzIiIHk9IjE2IiB3aWR0aD0iMzIwIiBoZWlnaHQ9IjE2MCIgZmlsbD0ibm9uZSIgc3Ryb2tlPSIjZTBlMGUwIiBzdHJva2UtbGluZWpvaW49InJvdW5kIiBzdHJva2Utd2lkdGg9IjgiLz4KIDxnIGZpbGw9IiNlMGUwZTAiPgogIDxjaXJjbGUgY3g9IjE1MiIgY3k9Ijk2IiByPSI4Ii8+CiAgPGNpcmNsZSBjeD0iMTkyIiBjeT0iOTYiIHI9IjgiLz4KICA8Y2lyY2xlIGN4PSIyMzIiIGN5PSI5NiIgcj0iOCIvPgogPC9nPgo8L3N2Zz4K');
   background-repeat: no-repeat;
   background-size: contain;
-  max-width: 100%;
+  display: block;
+  margin: 0 auto;
   width: 1200px;
+  max-width: 100%;
 }
 
-#visualization.placeholder #plot img {
+#visualization.placeholder #plot > img,
+#visualization.placeholder #plot > div {
   background-image: url('data:image/svg+xml;base64,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');
 }
 

visualizer/templates/plotter.html

@@ -86,7 +86,7 @@
            {#- #} src="{{ url_for('plot_image', name=g.plotter.name) -}}
                        ?{{ g.image_qs }}">
     {% else %}
-      <img aria-label="" src="data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSIxMjAwIiBoZWlnaHQ9IjYwMCI+PC9zdmc+">
+      <div></div>
     {% endif %}
     </div>
     <ul id="sources">