Is it possible to use multiple units in one line of CSS code? For example:
width: 20% + 5px;
Im presuming not. If so, how do you do it in a language such as javascript?
As Sirko pointed out, there is calc(). Unfortunately there is a catch with using that function: out of the major browsers IE <9 and Opera does NOT support it.
If all you want is to include a padding then you can achieve the same thing with the box-sizing attribute set to border-box that has far better browser support. For IE<8 there is also a polyfill available.
.span20 {
-moz-box-sizing: border-box;
box-sizing: border-box;
width: 20%;
padding: 5px;
float: left;
}
Here is a jsfiddle demonstrating the above.
It is possible using CSS calc():
width: -webkit-calc(20% + 5px);
width: -moz-calc(20% + 5px);
width: calc(20% + 5px);