If you are wanting to hide the text "Welcome", you would use:
. PostHeader { display:none; }
For welcome and the icon, you would use:
.PostHeaderIcon-wrapper {display:none; }
If the theme makes use of body classes, you should find additional classes on the <body> element that will help you target specific pages. See the body class function reference.
You can test these changes most quickly and easily using Firebug or Chrome/Safari developer tools. See YouTube for how to use Firebug.