Customizing Nivo caption and background

Hello,
This is an excellent plugin! I have a couple questions about fine-tuning it:
1. How do I customize caption style for Nivo? I tried this to remove rounded corners, but no luck:
.nivo-lightbox-theme-default .nivo-lightbox-title {
border-radius: 0px !important;
}

2. Is it possible to darken the background by increasing opacity? I tried this css (based on another post in the support forum), but it didn’t do it:

#nivo-lightbox-overlay {
background: #00000 !important;
}

#nivo-lightbox-action, #nivo-lightbox-caption {
overlay:90% !important;
}

Thank you!
Jen