Fix theme consistency, i18n completeness, CSS variable naming, and hardcoded strings

src/app/admin/writeable-boxes/page.tsx

@@ -47,7 +47,7 @@ export default async function AdminWriteableBoxes() {
 
       <section className="mt-6">
         <h2 className="admin-section-title">{t("newBox")}</h2>
-        <form action={createBox} className="grid cols-2">
+        <form action={createBox} className="grid grid-cols-1 gap-4 md:grid-cols-2">
           <div>
             <label htmlFor="new_title" style={{ display: "block", fontWeight: 700 }}>
               {t("form.name")}
@@ -127,7 +127,7 @@ export default async function AdminWriteableBoxes() {
                   </span>
                 </div>
 
-                <form action={updateBox} className="grid cols-2">
+                <form action={updateBox} className="grid grid-cols-1 gap-4 md:grid-cols-2">
                   <input type="hidden" name="id" value={String(box.id)} />
                   <div>
                     <label