How to make navigation bar transparent?

I’m currently using mantra theme. Found this code but not work for this theme:

/* Blend Menu Bar Into Header Image
------------------------------------------------------- */

#access {
-moz-box-shadow: 0 1px 2px rgba{0, 0, 0, 0.4};
background: -moz-linear-gradient{#252525, #QAQAQA} repeat scroll 0 0 transparent;
clear: both;
display: block;
float: left;
margin: -40px auto 6px;
opacity: 0.50;
width: 100%;
z-index: 1000;
}

#branding img {
height: 270px;
margin-bottom: -7px;
width: 100%;
z-index: 1;
}

This is my website, Sample. How to make menu bar become transparency??