[css] font-weight is not working properly?

font-weight can also fail to work if the font you are using does not have those weights in existence – you will often hit this when embedding custom fonts. In those cases the browser will likely round the number to the closest weight that it does have available.

For example, if I embed the following font...

@font-face {
    font-family: 'Nexa';
    src: url(...);
    font-weight: 300;
    font-style: normal;
}

Then I will not be able to use anything other than a weight of 300. All other weights will revert to 300, unless I specify additional @font-face declarations with those additional weights.