CB

Real issue is in CB templates (default at least):

.dynamic-tab-pane-control .tab-page .tab-content {
    margin: 10px;
}

does not set width: auto.

then as:

form.cb_form                            , .cb_tab_content                                {    width: 100%;    margin: 0px;    padding: 0px;    border-width: 0px;    }

Does set width 100%, that setting is not overridden, while the margin is. So we end up too wide.

CB r1200 and coolness/mycommunity r1504 fixes this bug and the related bug #2021 .