Disable border for all Portlet in liferay

liferay-look-and-feel.xml (tomcat\webapps\ROOT\WEB-INF)

Add the following setting in liferay-look-and-feel.xml for disabling border for all portlets by default.

<theme id="classic" name="classic">
       <settings>
            <setting key="portlet-setup-show-borders-default" value="false" />
        </settings>
</theme>


or

Portal-ext.properties (tomcat\webapps\ROOT\WEB-INF)

You can change it through property file also by adding this entry:

theme.portlet.decorate.default=false