This CSS code creates a gradient effect for the background of elements with the class name "gradient". Here is an explanation of each line of code: 1. `background: -webkit-gradient(linear, left top, left bottom, from(#000000), to(#ffffff));` - This line applies a linear gradient from top to bottom using WebKit browsers like Safari and older versions of Chrome. It transitions from the color #000000 (black) to #ffffff (white). 2. `background: -moz-linear-gradient(top, #000000, #ffffff);` - This line applies a linear gradient from top to bottom using Mozilla browsers like Firefox. It also transitions from the color #000000 to #ffffff. 3. `filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#000000', endColorstr='#ffffff');` - This line creates a gradient for IE browsers using the proprietary filter property. It transitions from the color #000000 to #ffffff. By combining these three lines, the code ensures that the gradient effect will be displayed consistently across different browsers that support these specific syntaxes for creating gradients.