Here are some ways you might use "absolutely" with "casual" depending on the intended meaning:
To emphasize the casualness:
* "I'm feeling absolutely casual today, so let's just hang out in sweatpants and watch movies."
* "He dressed absolutely casually for the party, which surprised everyone who expected him to be in a suit."
To express strong agreement with a casual suggestion:
* "Let's just grab some pizza and hang out. Absolutely casual, no pressure."
* "Should we meet at the coffee shop or just have a casual chat online? Absolutely casual, whatever works for you."
To describe a situation where any level of formality is out of place:
* "This is an absolutely casual get-together, just come as you are."
* "The atmosphere at the event was absolutely casual, everyone was laughing and enjoying themselves."
Remember, "absolutely" often adds a strong emphasis, so use it judiciously. In some cases, simply "casual" might be sufficient.