fix(styles): make announcement bar span full viewport width

Use transform-based centering (left: 50% + translateX(-50%)) to break
out of parent container margins and span edge to edge.

Author: profvjreddi

book/quarto/assets/styles/style.scss

@@ -416,8 +416,16 @@ a {
   border-color: rgba($crimson, 0.4) !important;
   border-left: 4px solid $crimson !important;
   color: darken($crimson, 25%) !important;
-  width: 100% !important;
-  max-width: 100% !important;
+  // Break out of parent container to span full viewport width
+  // Transform-based centering ignores parent margins
+  position: relative !important;
+  left: 50% !important;
+  transform: translateX(-50%) !important;
+  width: 100vw !important;
+  max-width: 100vw !important;
+  margin-left: 0 !important;
+  margin-right: 0 !important;
+  box-sizing: border-box !important;
 
   // Dismiss button (X)
   .btn-close {