rgba(51, 170, 51, .1) /* 10% opaque green */<br /> rgba(51, 170, 51, .4) /* 40% opaque green */<br /> rgba(51, 170, 51, .7) /* 70% opaque green */<br /> rgba(51, 170, 51, 1) /* full opaque green */

background: rgba(255, 255, 255, 0.25);

background-color: #ff000088; <— the 88 is the alpha<br /> background-color: #ff0000 50%;

/* css semi-transparent background color */<br /> .bg-semi-transparent {<br /> background-color: #ffffff40!important;<br /> /* change numbers from 00 to 99 at last of hex code<br /> for transpency you want. */<br /> }

h1 {background-color:rgba(255,0,0,0.3);}