How to modify a specific header style?

[tong123123]

as the attached jpg shown, I want to apply style on the "add" button header, which is a Header of ActionCell.
the ActionCell is named addPCCell, but I find there is no any addStyleName, setStyleName or related method.
the Header is name footerAdd, and I also find footerAdd has no any addStyleName, setStyleName or related method.
The column of the header is named removeBtnCol, it has setCellStyleNames, but has no effect on the Header!! and there is no any setHeaderStyleName or related method,
so how to modify the specific column Header and its ActionCell?

for css, I can apply on all button and all THeader, but not a specific button on addPCCell and a specific Column Header
the css is something like

.central-runtime-debug-log-webapp .datagrid button{
    height:22px;
    width:55px;
    font-size: 11px !important;       
}

.central-runtime-debug-log-webapp .datagrid thead th{
    background-color: #D7E5F5;
    color:  #15428B;
    font-family: Arial Unicode MS, Arial, sans-serif;
    font-size: small;
    padding-right:5px;
    padding-left:5px;   
}

[tong123123]

the topic in
https://groups.google.com/forum/?fromgroups=#!topic/google-web-toolkit/bBe7GCVoVWQ
may be useful, but all the link inside return error 404.

[tong123123]

So trouble, Header and ActionCell is not inherited UIObject, so cannot use ensureDebugId to give a specific header and actioncell an id to apply css!!

[tong123123]

I use pure css to finish it finally.
to select a specific header, like the second header column, I use

.projectCdGrid thead th:nth-of-type(2)

for the button in thead, I use

.projectCdGrid thead th button

hope this can help others with simiilar problem.