It looks like you tried
.wp-caption p.wp-caption-text, #content .gallery .gallery-caption,.entry-attachment .entry-caption .wp-caption-text {font: normal}
But the right CSS rule is
.wp-caption p.wp-caption-text, #content .gallery .gallery-caption,.entry-attachment .entry-caption .wp-caption-text {font-style: normal}
When you have a doubt on CSS syntax, there are plenty of good CSS reference sites on google you can use like the ones at the bottom of the post below