Feat: Add background-core-standard to tailwind.css #3221 (#6437)

### What problem does this PR solve?

Feat: Add background-core-standard to tailwind.css #3221

### Type of change


- [x] New Feature (non-breaking change which adds functionality)

web/tailwind.css

@@ -45,6 +45,7 @@
     --colors-background-functional-solid-danger: rgba(222, 17, 53, 1);
     --colors-background-core-strong: rgba(98, 72, 246, 1);
     --colors-background-sentiment-solid-primary: rgba(127, 105, 255, 1);
+    --colors-background-core-standard: rgb(90, 75, 254);
 
     --button-blue-text: rgb(22, 119, 255);