[css] Why is vertical-align:text-top; not working in CSS

You can use contextual selectors and move the vertical-align there. This would work with the p tag, then. Take this snippet below as an example. Any p tags within your class will respect the vertical-align control:

#header_selecttxt {
    font-family: Arial;
    font-size: 12px;
    font-weight: bold;
}

#header_selecttxt p {
    vertical-align: text-top;
}

You could also keep the vertical-align in both sections so that other, inline elements would use this.