Style.css too powerful selector used

In your selectors, you should replace
#primary #content
to
#content

Example selectors in style.css:

#primary #content h2 {
    font-family: "bebas";
    font-size: 30px;
    font-weight: 400;
    text-shadow: 1px 1px 1px rgba(255, 255, 255, 0.5);
}

#primary #content article img {
    border: 1px solid #fff;
    box-shadow: 1px 1px 0 0 rgba(157, 193, 24, 1);
    max-width: 99%;
}

This could help to avoid issues with custom codes in the article which added with shortcode.