feat: add welcome overlay CSS styles to main stylesheet

- Add consistent styling for welcome overlay components
- Use application color scheme (#1f2937, #4b5563)
- Maintain visual consistency with rest of application
- Proper z-index and transitions for smooth UX

src/styles.css

@@ -48,6 +48,47 @@
 }
 
 /* Correct and incorrect answer styles */
+
+/* Welcome overlay styles */
+.welcome-overlay {
+  position: fixed;
+  top: 0;
+  left: 0;
+  width: 100%;
+  height: 100%;
+  background: rgba(0, 0, 0, 0.8);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  z-index: 1000;
+  opacity: 0;
+  transition: opacity 0.3s ease;
+}
+
+.welcome-modal {
+  background: white;
+  border-radius: 12px;
+  padding: 32px;
+  box-shadow: 0 20px 40px rgba(0, 0, 0, 0.3);
+}
+
+.welcome-title {
+  margin: 0 0 24px 0;
+  color: #1f2937;
+  font-size: 28px;
+  font-weight: 600;
+}
+
+.welcome-content {
+  text-align: left;
+  color: #4b5563;
+  line-height: 1.6;
+  margin-bottom: 32px;
+}
+
+.welcome-content p {
+  margin: 0 0 16px 0;
+}
 .cloze-input.correct {
   background-color: #dcfce7 !important;
   border-color: #16a34a !important;