Move all the root styles to fragment files

Create assets/styles/root to hold all the fragments of the root
stylesheet. This should make it easier to find and hack on style. Yay!

assets/styles/root/099_utility.css

@@ -0,0 +1,26 @@
+@layer utility {
+    .centered { text-align: center; }
+    .float-right { float: right; }
+
+    .nobreak { white-space: nowrap; }
+    .noselect {
+        cursor: default;
+        -webkit-user-select: none;
+        -moz-use-select: none;
+        -ms-user-select: none;
+        user-select: none;
+    }
+
+    .platter {
+        -webkit-backdrop-filter: var(--platter-backdrop-filter);
+        backdrop-filter: var(--platter-backdrop-filter);
+        background-color: var(--platter-background-color);
+        border: 1px solid var(--header-border-color);
+        border-radius: 12px;
+        box-shadow: 3px 4px 4px var(--header-box-shadow-color);
+    }
+
+    .visible { visibility: visible; }
+
+    article.two-column { columns: 2; }
+}