I have added some contents using blocks in drupal 7. I need to give custom styles like width, position, color etc
You have in your site a generic template of block (yoursite/modules/block/block.tpl.php). Copy this file, and paste it in your template folder. If you want to assign it to a specific block, you just have to rename it like : block--machine-name-of-your-block.tpl.php
Then you have to edit this template to customize it.