A sure fire way is

> select
> description
> from
> items
> where
> upper(description) containing 'COMPUTER'
>
>

Actually, the upper is not needed.

select description
from items
where description containing 'computer'

returns all rows where description has the word 'computer' within the
data regardless of case.

'Computer', 'COMpuTer', etc.

neither is the case important in the input string literal after
"containing".
Of course, I have no idea why this is so, but it is.

Also, tt may be important to note that neither your option, nor this one
can use an index, a table scan will occur.