Disable child theme css on certain pages

There are two methods to accomplish what you what need to do.

METHOD 1

The first method is to create a separate stylesheet from your child’s main style.css, and then move all your css into that stylesheets. For this example, lets call this stylesheet custom-style.css.

As said, copy all the css that will be specific to only certain pages to this new stylesheet.

You can now enqueue this new stylesheet using wp_enqueue_style() conditionally using the is_page() conditional tag, only for the pages that you need. So open up your child functions.php and add the following in there

function enqueue_my_style() {
  if( is_page( SEE CODEX FOR EXAMPLES)) {
    wp_enqueue_style( 'my-style', get_stylesheet_directory_uri().'/custom-style.css' );
  }
 }
 add_action( 'wp_enqueue_scripts', 'enqueue_my_style' );  

METHOD 2

Default body_class() makes a few css selector available by default to target specific pages using css. Here are these selectors

• .rtl {}
• .home {}
• .blog {}
• .archive {}
• .date {}
• .search {}
• .paged {}
• .attachment {}
• .error404 {}
• .single postid-(id) {}
• .attachmentid-(id) {}
• .attachment-(mime-type) {}
• .author {}
• .author-(user_nicename) {}
• .category {}
• .category-(slug) {}
• .tag {}
• .tag-(slug) {}
• .page-parent {}
• .page-child parent-pageid-(id) {}
• .page-template page-template-(template file name) {}
• .search-results {}
• .search-no-results {}
• .logged-in {}
• .paged-(page number) {}
• .single-paged-(page number) {}
• .page-paged-(page number) {}
• .category-paged-(page number) {}
• .tag-paged-(page number) {}
• .date-paged-(page number) {}
• .author-paged-(page number) {}
• .search-paged-(page number) {}

When applying styles to specific elements, you can use these selectors to target specific elements for specific pages only, for instance

.home H1 {}

will only target the H1 element on the homepage