refactor: Update layout and styling components; remove unused CSS files and enhance button styles

frontend/vue-app/src/layout/AuthLayout.vue

@@ -36,15 +36,88 @@ const showBack = computed(
 </script>
 
 <style scoped>
-/* Only keep styles unique to ChildLayout */
+.layout-root {
+  width: 100%;
+  min-height: 100vh;
+  height: 100vh;
+  display: flex;
+  flex-direction: column;
+  padding: 0;
+  background: var(--header-bg, linear-gradient(135deg, #667eea 0%, #764ba2 100%));
+}
 
-.topbar > .spacer {
+.topbar {
+  display: flex;
+  align-items: stretch;
+  padding: 0;
+  height: 48px;
+  width: 100%;
+  box-sizing: border-box;
+}
+
+.back-btn-container {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 65px;
+  min-width: 65px;
+  max-width: 65px;
+  height: 48px;
+  min-height: 48px;
+  max-height: 48px;
+  margin-left: 5px;
+  margin-right: 5px;
+  box-sizing: border-box;
+}
+
+.back-btn {
+  width: 65px;
+  min-width: 65px;
+  max-width: 65px;
+  height: 48px;
+  min-height: 48px;
+  max-height: 48px;
+  margin: 0;
+  background: var(--button-bg, #fff);
+  border: 0;
+  border-radius: 8px 8px 0 0;
+  cursor: pointer;
+  color: var(--button-text, #667eea);
+  font-weight: 600;
+  font-size: 0.8rem;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  box-sizing: border-box;
+  overflow: hidden;
+  padding: 0;
+  transition:
+    background 0.18s,
+    color 0.18s;
+}
+
+@media (max-width: 480px) {
+  .back-btn {
+    font-size: 0.7rem;
+  }
+}
+
+.spacer {
+  flex: 1 1 auto;
   height: 100%;
   display: flex;
   align-items: center;
 }
 
-.spacer {
+.main-content {
   flex: 1 1 auto;
+  width: 100%;
+  justify-content: center;
+  align-items: flex-start;
+  box-sizing: border-box;
+  min-height: 0;
+  height: 0;
+  overflow: hidden;
+  overflow-y: visible;
 }
 </style>