随意 can be positive (relaxed, casual, easygoing) or negative (careless, too casual). Context determines the tone. 穿得很随意 could mean 'dressed casually' or 'dressed sloppily.'
usage
随便 (suíbiàn) is similar and more colloquial. 随意 is slightly more refined. Both can mean 'whatever you want' or 'carelessly' depending on context.
