Casual Lolita (カジュロリ) is any style of Lolita that is more toned down, while still retaining the basic Lolita elements. It is very hard to put together a nice Casual Lolita outfit unless you have years of experience or are a natural at it.
Most favoured in the Casual Lolita outfits is (in a way) simplicity, so a nice simple cutsew perhaps with a motif of some sort paired with a lolita skirt and hair accessory/headdress (however the hair accessories are usualy toned-down as well.)
Casual Lolita can best be described as what a Lolita would wear when not 'dressing up.' Still modest, and elegant but not as over the top as most other Lolita styles.
A great Casual Lolita can be compiled out of any colour, as long a you remember to match colours, prints, etc. etc. as you would with any other Lolita style. A simple caridgan over a jsk or skirt creates a nice casual look.