First of all, please search your question before posting. You can find your answer here
Secondly next time you ask a question, if you cannot find it while you search it, would be great if you would try to create at least a working example (using code sample).
In the third row, you should really take in consideration if using !important is a good ideea. You can read more about this topic here.
Also would be better if you use more classes and less id's while working with css. id's should be used only when you are really sure you want some code something only on a single element from all your code.
Avoiding using spaces in your id's and classes would also be a great ideea so you avoid this kind of problems in the future.
Edit: here is a working example of your example since you said that is not working :)
input#id-Output\ Url{
font-weight: bold!important;
}
<input id="id-Output Url" />