Add unit tests for LoginButton component with comprehensive coverage

frontend/vue-app/src/assets/styles.css

@@ -1,12 +1,3 @@
-/* Edit view container for forms */
-.edit-view {
-  max-width: 400px;
-  margin: 2rem auto;
-  background: var(--form-bg);
-  border-radius: 12px;
-  box-shadow: 0 4px 24px var(--form-shadow);
-  padding: 2rem 2.2rem 1.5rem 2.2rem;
-}
 /*buttons*/
 .btn {
   font-weight: 600;
@@ -119,3 +110,29 @@
   font-size: 1rem;
   margin-top: 0.5rem;
 }
+
+.modal-backdrop {
+  position: fixed;
+  inset: 0;
+  background: rgba(0, 0, 0, 0.45);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  z-index: 1200;
+}
+
+.modal {
+  background: var(--modal-bg);
+  color: var(--modal-text);
+  padding: 1.25rem;
+  border-radius: 10px;
+  width: 360px;
+  max-width: calc(100% - 32px);
+  box-shadow: var(--modal-shadow);
+  text-align: center;
+}
+
+.modal h3 {
+  margin-bottom: 0.5rem;
+  font-size: 1.05rem;
+}