Tumblr – How to Remove ‘Follow,’ ‘Unfollow,’ and ‘Join Tumblr’ Buttons

You can add custom CSS to your theme without modifying it by going to Customize -> Advanced.

Hence to add a grey background to your <code> you can paste this in the "Add custom CSS" textarea:

pre, code {
 background-color: LightGrey;
}

I used the fact that the {PostID} variable is empty for static pages.

So declare a CSS class like this:

.hiddenOnStaticPages {
    display: none;
}

Then wrap the comments link (and the actual comments) in a div like this:

<div class="hiddenOnStaticPages{PostID}">
Comment HTML goes here...
</div>