Here’s an example of using <ltng:require>:
<ltng:require styles="{!$Resource.resourceName}" />
resourceName is the Name of the static resource. In a managed packaged, the resource name must include the package namespace prefix, such as $Resource.yourNamespace__resourceName. For a stand-alone static resource, such as an individual graphic or script, that’s all you need. To reference an item within an archive static resource, add the rest of the path to the item using string concatenation.
Here are some considerations for loading styles:
<ltng:require> also has a scripts attribute to load a list of JavaScript libraries. The afterScriptsLoaded event enables you to call a controller action after the scripts are loaded. It's only triggered by loading of the scripts and is never triggered when the CSS in styles is loaded.
For more information on static resources, see “Static Resources” in the Salesforce online help.
<ltng:require styles="{!$Resource.bootstrap}"/> <div class="myBootstrap"> <c:myComponent /> <!-- Other component markup --> </div>