Collection widget css not working

Hello All,

I gave some css code for the cell mashup, It is working fine when we opened the cell mashup separately.

But the same cell mashup css not working, when it is used in the collection widget.

I have mentioned the css code for you reference.

.myBoxColumnLeft .widget-fieldset .widget-flexcontainer {
border-color: #d9d9d9;
border-style :solid;
border-width:1px 1px 1px 1px;
background-color:#efefef;
}

Can anybody give the solution for this?