style: unify form element styles in common.css, redesign focus rings, refactor public search bar, tweak admin section

app/public/assets/css/variables.css

@@ -101,6 +101,9 @@
     --border-primary: #dddddd;
     --border-secondary: #cccccc;
 
+    /* Border radius */
+    --radius: 10px;
+
     /* Status */
     --success: #5cd69d;
     --error: #f25a5a;