[graph] fix tree/toolbar positioning

Scrolling of tree did cause scrolling of top controls. Now the controls
are fixed.

dist/styles/Graph.css

@@ -12,7 +12,7 @@
   max-width: 200px;
 }
 #graph-explorer #toggle-container {
-  position: absolute;
+  position: fixed;
   z-index: 999;
   right: 25%;
   top: 10px;
@@ -22,7 +22,7 @@
   padding-top: 90px;
 }
 #graph-explorer #controls-container {
-  position: absolute;
+  position: fixed;
   z-index: 999;
   backdrop-filter: blur(4px);
   background: rgba(255, 255, 255, 0.75);

dist/styles/Graph.sass

@@ -19,7 +19,7 @@
         max-width: 200px
 
   #toggle-container
-    position: absolute
+    position: fixed
     z-index: 999 // needs to appear above solid menu bar
     right: 25%
     top: 10px
@@ -28,7 +28,7 @@
       padding-top: 90px
 
   #controls-container
-    position: absolute
+    position: fixed
     z-index: 999 // needs to appear above graph elements
     backdrop-filter: blur(4px)
     background: rgba(255,255,255,75%)