Hauptfenster: Header fest, nur Inhalt scrollt

src/style.css

@@ -29,13 +29,25 @@
   box-sizing: border-box;
 }
 
+html,
+body {
+  height: 100%;
+}
+
 body {
   margin: 0;
 }
 
+#app {
+  display: flex;
+  flex-direction: column;
+  height: 100vh;
+}
+
 /* ---------- Header ---------- */
 
 header {
+  flex: none;
   display: flex;
   align-items: center;
   gap: 1.5rem;
@@ -110,6 +122,8 @@ input[type="checkbox"] {
 }
 
 main {
+  flex: 1;
+  overflow-y: auto;
   padding: 1.5rem;
 }