adding document mode

I've been thinking a lot about the treehouse and I feel like it's time to say goodbye to the tree format.

static/css/tree.css

@@ -2,7 +2,6 @@
 
 :root {
     --tree-indent-width: 3.2rem;
-    --transition-duration: 0.15s;
     --button-bar-icon-size: 2.8rem;
 }
 
@@ -82,6 +81,21 @@
 .tree {
     --tree-indent-guide-dim: transparent;
     --tree-indent-guide-highlighted: transparent;
+
+    display: flex;
+    flex-direction: column;
+
+    align-self: start;
+    align-items: center;
+
+    & > article {
+        padding: 1.6rem;
+        width: 100%;
+    }
+
+    & > footer {
+        max-width: none;
+    }
 }
 
 .tree:has(.branch-container:hover) {
@@ -116,8 +130,9 @@
 }
 
 /* Top level should not have an indent or a border. */
-.tree > ul {
+.tree article > ul {
     padding-left: 0;
+    margin-left: 0;
     border-left: none;
 }