Allow panel to be scrolled again

This is a quick fix for a major bug: the object list is currently not
scrollable.

Closes #586

Re-introduce `overflow-y: auto` so panel can be scrolled when there are
many objects.

media/src/Panel.svelte

@@ -234,7 +234,7 @@
 
     const onResizePanel = function(e) {
         if (isPanelResizing) {
-            const newWidth = e.clientX - 10;
+            const newWidth = e.clientX - 16;
             if (newWidth >= 300 && newWidth <= window.innerWidth * 0.6) {
                 panelWidth = newWidth;
             }
@@ -299,18 +299,7 @@
             }
         }
 
-        // Observe panel width to place panel-buttons properly.
-        // Annoying-ish solution, but it works.
-        const resizeObserver = new ResizeObserver(entries => {
-            for (let entry of entries) {
-                if (entry && entry.contentRect && entry.contentRect.width) {
-                    panelWidth = entry.contentRect.width;
-                }
-            }
-        });
-
-        const panelEl = document.querySelector('.demos-panel');
-        resizeObserver.observe(panelEl);
+        panelEl = document.querySelector('.demos-panel');
 
         window.addEventListener('pointermove', onResizePanel);
         window.addEventListener('pointerup', onResizePanelEnd);
@@ -776,22 +765,21 @@
     .demos-panel {
         z-index: 1;
 
-        position: fixed;
-
         min-width: 300px;
         max-width: 60%;
 
         background-color: transparent;
 
-        resize: horizontal;
+        overflow-y: auto;
+        overflow-x: hidden;
     }
 
     .panel-button {
         cursor: pointer;
         position: absolute;
 
-        min-width: 25px;
-        height: 40px;
+        min-width: 28px;
+        height: 38px;
 
         z-index: 2;
     }
@@ -810,7 +798,7 @@
     }
 
     .panel-button.panel-resizer {
-        top: 86px;
+        top: 82px;
         cursor: col-resize;
     }