Gnome Shell theme and box-shadow

[Flavien Lambert <petit lepton gmail com>]

Hi everyone, I am playing with the Gnome Shell theme, creating my own css file. I am facing a weird problem related to the use of box-shadow. I try to put a shadow on buttons in the following way:

.candidate-page-button,
.notification-button,
.notification-icon-button,
.hotplug-notification-item,
.hotplug-resident-eject-button,
.modal-dialog-button{
    color: #ffffff;
    background-gradient-start : #4a90d9;
    background-gradient-end : #4a90d9;
    border-radius: 0px;
    border: 0px;
    box-shadow : 0px 0px 5px black;
}

but the shadow is totally messy, creating strange patterns. The shadow is fine on

.system-menu-action {
    background-color : #4a90d9;
    color: white;
    border: 0px;
    padding: 13px;
    box-shadow : 0px 0px 5px #000000;
}

Any hints?

Thanks,

F.