Match Angular back button: full-width blue fill, white text

Angular ships '← Вернуться к Онлайн-Табло' as a solid 48px-tall
primary button spanning the full 285px mini-list column (bg #4A90E2,
white text, 3px radius). React had it as a narrow pale-blue badge
(bg #E3F0FF, dark-navy text, 35px tall), which read as a secondary
link rather than the primary navigation affordance above the
sibling-flights list. Retune DetailsBackButton to the measured
Angular values.

src/features/online-board/components/DetailsBackButton/DetailsBackButton.scss

@@ -1,18 +1,25 @@
+// Angular renders the back link as a full-width solid button above the
+// flights mini-list — same 285px column, blue fill, white text, 48px
+// tall. Match that.
 .details-back-button {
-  display: inline-flex;
+  display: flex;
   align-items: center;
+  justify-content: center;
   gap: 8px;
-  padding: 8px 16px;
-  background: #e3f0ff;
-  color: #1a3a5c;
-  border-radius: 6px;
+  width: 100%;
+  min-height: 48px;
+  padding: 12px 16px;
+  background: #4a90e2;
+  color: #fff;
+  border-radius: 3px;
   text-decoration: none;
   font-size: 14px;
   font-family: inherit;
   cursor: pointer;
 
   &:hover {
-    background: #c7dff5;
+    background: #3a7cc8;
+    color: #fff;
   }
 
   &__arrow {