How to make blog post respnsive in home page

Hi,
How can I make the home page blog post (including image) responsive? I used this;
.

post_content img {
width: 100%;
height: auto;
}

But nothing happened, and the blog post in the home page isn't mobile adaptable. How can you aid me to solve this?
url:http://goodtidingshospital.com

Regards