Not overriding plugin css

I’m using Porfolio Gallery plugin ant the thumbnail images have height and width attributes with !important. I tried this plugin but the css it injects is still being overridden by the plugin. when I click the element inspector, I can see my custom css below and crossed out. The css I am trying to override is somehow being added to the end of the index file. What can I do?

https://wordpress.org/plugins/simple-custom-css/