Hi Jan,
That will work on blog post content images added through Gutenberg editor’s image block.
To clarify: With blog posts images, did you mean the post thumbnail images on the Blog index page and archive pages?
If yes, try adding this CSS:
.post-image {
border-radius: 30px;
overflow: hidden;
}
.post-image img {
display: flex;
}
If it’s for the single post page’s featured image, try this CSS:
.featured-image {
border-radius: 30px;
overflow: hidden;
}