Edit in JSFiddle

body { font-family: sans-serif; color: #ccc; background: #111;}
:checked + label {
    color: lime;
}
label + label {
    padding-left: 1em;
    opacity: 0.1;
    visibility: hidden;
    transition: 0.5s;
}
:checked + label ~ label  {
    opacity: 1;
    visibility: visible;
}
input {width: 3em;}

<form>
    <input type="checkbox" id="moo" /><label for="moo">Condition</label>
    <label>
        value for condition: 
        <input type="text" value="20">
     </label>
</form>