entry summary trouble

And it sure is troubling lol. Pulling my hair out even. Have tweaked themes with css but first attempt at building one from the bottom up.

Anyway, Thought everything was done but when I clicked on the tags they come up with full size images. So I attempted to insert a divclass into the entry summery so I could set the width to 300px and inline block them to it grided out.

No go whatso ever. Can not do anything with css, not only width or img width but borders, shadows nothing. Know I am in the right place as I see the mmmmmmm on the tag pages but not single posts or pages, know it’s picking up the div I see the dddddddd. Tried moving it all around, encasing the content only, by itself on top and botton, nooooooooooothing. What in Hades am I doing wrong? Please help me while I still have hair lol.

<div class="megart">ddddddddd
<section class="entry-summary">
<?php the_content(); ?>
<?php if( is_search() ) { ?><div class="entry-links"><?php wp_link_pages(); ?></div><?php } ?>
</section>mmmmmmmmm
</div>

might not have correct css string. using
.megart
might need something longer stringing together the levels. something I’ve never dealt with.