💄(react) update DatePicker segments colors

Based on QA feedbacks we just want a background color for the focused
segments.

.changeset/modern-badgers-draw.md

@@ -0,0 +1,5 @@
+---
+"@openfun/cunningham-react": minor
+---
+
+add a background color to DatePicker segments

packages/react/src/components/Forms/DatePicker/index.scss

@@ -70,6 +70,11 @@
         &--empty {
           color: var(--c--components--forms-field--color);
         }
+
+        &:focus-visible {
+          background-color: var(--c--theme--colors--primary-100);
+          outline: none;
+        }
       }
     }