Header Image Box-Shadow

On my site Tiny House Report I have the TwentyTwelve box-shadow – and I need to have it go bye-bye.

I have tried

.entry-content img, .comment-content img, .widget img, img.header-image, .author-avatar img, img.wp-post-image {
border-radius: 0;
box-shadow: none;
}

.entry-content img, .comment-content img, .widget img, img.header-image, .author-avatar img, img.wp-post-image {
border-radius:0 !important;
box-shadow: none !important;
}

I went into the parent css and changed it and it worked perfectly.

However, for some reason my child theme will not override the parent theme and my brain is in meltdown mode.

Can someone show me how to persuade my child theme css to get rid of the box-shadow in my header?