Where do I write the css code for the Block Class module

Hi

I am new to Drupal and CSS. I want to put a border around one block. I have installed the block class module & defined a css class. I am using the Adaptive theme so have tried writing the class into mysubtheme/css/global.styles.css. But nothing seems to work. I can get a border around all the blocks, but not the one I have defined the css class for. Please can someone advise on where to put the code and what the code should contain.

All I have go so far is outline-style: groove; outline-color: blue; outline-width: thin;

Many thanks

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