docs: update website brand colors (#417)

Author: chenjiahan

website/theme/theme.scss

@@ -1,10 +1,10 @@
 :root {
-  --rp-c-brand: #f93920;
-  --rp-c-brand-light: #fa6552;
-  --rp-c-brand-lighter: #fc9183;
-  --rp-c-brand-dark: #f82307;
-  --rp-c-brand-darker: #e01f06;
-  --rp-c-brand-tint: rgba(249, 57, 32, 0.15);
+  --rp-c-brand: #ff5e00;
+  --rp-c-brand-dark: var(--rp-c-brand);
+  --rp-c-brand-darker: #ff704d;
+  --rp-c-brand-light: #ff7524;
+  --rp-c-brand-lighter: #ff7524;
+  --rp-c-brand-tint: rgba(255, 94, 0, 0.07);
   --rp-c-text-code: var(--rp-c-text-1);
 }