First step in customizing AWP is to create a folder in the customization folder. For example C:\Program Files\Canto\Cumulus Web Solutions\apache-tomcat-8.0.36\webapps\awp\customizations\mycompanyname
Go to \awp\css and copy the customer.css files to your customization folder and keep the correct path to the css file like this: \awp\customizations\mycompanyname\css\customer.css
Edit the customer.css (by default it should be empty) and insert the elements you would like to change for example:
.boxtoggle__title, .click-target { color: #fff; }
Save the css file. To apply the new css either restart the Cumulus Web Solutions service or save the AWP settings in the ServerConsole which triggers a settings reload.