[css] Is it possible to use an input value attribute as a CSS selector?

You can use Css3 attribute selector or attribute value selector.

/This will make all input whose value is defined to red/

input[value]{
color:red;
}

/This will make conditional selection depending on input value/

input[value="United States"]{
color:red;
} 

There are other attribute selector like attribute contains value selector,

input[value="United S"]{
color: red;
}

This will still make any input with United state as red text.

Than we attribute value starts with selector

input[value^='united']{
color: red;
}

Any input text starts with 'united' will have font color red

And the last one is attribute value ends with selector

input[value$='States']{
color:red;
}

Any input value ends with 'States' will have font color red