https://theme-ui gradients code example
Example: ui gradient
background: #000428; /* fallback for old browsers */
background: -webkit-linear-gradient(to bottom, #000428, #004e92); /* Chrome 10-25, Safari 5.1-6 */
background: linear-gradient(to bottom, #000428, #004e92); /* W3C, IE 10+/ Edge, Firefox 16+, Chrome 26+, Opera 12+, Safari 7+ */