fix(ui): avoid wrong body background color

Author: TkDodo

static/app/styles/global.tsx

@@ -142,6 +142,16 @@ const styles = (theme: Theme, isDark: boolean) => css`
     background: ${theme.tokens.background.primary};
   }
 
+  /*this updates styles set by base.less to match our theme*/
+  body.theme-dark {
+    background: ${theme.tokens.background.primary};
+  }
+  body.theme-system {
+    @media (prefers-color-scheme: dark) {
+      background: ${theme.tokens.background.primary};
+    }
+  }
+
   abbr {
     ${theme.tooltipUnderline()};
   }