how change body background bootstrap 4 code example
Example 1: bootstrap background color
.bg-primary
.bg-secondary
.bg-success
.bg-danger
.bg-warning
.bg-info
.bg-light
.bg-dark
.bg-white
Example 2: bootstrap 4 bg
.bg-gradient-primary
.bg-gradient-secondary
.bg-gradient-success
.bg-gradient-danger
.bg-gradient-warning
.bg-gradient-info
.bg-gradient-light
.bg-gradient-dark