How to change bg color in html5

Answer 1

go to css
select any element
type this
body {
background-color: green;
}

Answer 2

.class{
background:yellow;
}
#id{
background:red;
}
p{
background:skyblue;
}

Answer 3

With CSS.
Inline
<tag style="background-color:nameOrHexForColorOrRGB;">
Internal
<style>
tag or .className or #id
{
background-color:colorNameOrRGBoOrHex;
}
</style>
Or external, same command tha internal, but remove Style tag, and on html include:
<link type"stylesheet" href="pathOfCSSFile">