Increase dark-mode button contrast

The primary button's text and the secondary button's border were both
low-contrast against the teal/dark backgrounds in dark mode. Bump them
to match the higher-contrast treatment on reactnative.dev:

- primary text: dark:text-secondary (#404756) -> dark:text-gray-95 (#16181D)
- secondary border: #404756 -> #4E5769 (matches RN's rgb(78,86,104))

Primary button text contrast goes from ~4.6:1 to ~8.9:1. Dark mode only.

Author: aurorascharff

src/components/ButtonLink.tsx

@@ -33,7 +33,7 @@ function ButtonLink({
     className,
     'active:scale-[.98] transition-transform inline-flex font-bold items-center outline-none focus:outline-none focus-visible:outline focus-visible:outline-link focus:outline-offset-2 focus-visible:dark:focus:outline-link-dark leading-snug',
     {
-      'bg-link text-white dark:bg-brand-dark dark:text-secondary hover:bg-opacity-80':
+      'bg-link text-white dark:bg-brand-dark dark:text-gray-95 hover:bg-opacity-80':
         type === 'primary',
       'text-primary dark:text-primary-dark shadow-secondary-button-stroke dark:shadow-secondary-button-stroke-dark hover:bg-gray-40/5 active:bg-gray-40/10 hover:dark:bg-gray-60/5 active:dark:bg-gray-60/10':
         type === 'secondary',

tailwind.config.js

@@ -47,7 +47,7 @@ module.exports = {
       'outer-border': '0 0 0 1px rgba(0, 0, 0, 0.1)',
       'outer-border-dark': '0 0 0 1px rgba(255, 255, 255, 0.1)',
       'secondary-button-stroke': 'inset 0 0 0 1px #D9DBE3',
-      'secondary-button-stroke-dark': 'inset 0 0 0 1px #404756',
+      'secondary-button-stroke-dark': 'inset 0 0 0 1px #4E5769',
       none: 'none',
     },
     extend: {