RewriteEngine on
RewriteBase /
RewriteCond %{REQUEST_FILENAME} \.(gif|jpe?g|png|js|css|pdf)$ [OR]
RewriteCond %{REQUEST_FILENAME} -s [OR]
RewriteCond %{REQUEST_FILENAME} -l [OR]
RewriteCond %{REQUEST_FILENAME} -d

RewriteRule ^.*$ - [NC,L]

RewriteRule ^(.*) index.html [NC,L]