Setting table column width

[NotionCommotion]

Can anyone let me know how to set the width of all columns to 50px except the first row which should be 100px? I thought I would first set them all to 50, and then assign a class to the first row and set that one to 100, but it doesn't seem to work (see below). Thanks

#table_id td {border: 1px solid; width: 50px;}
td.first_column { width: 100px; font-weight: bold; }
.top_row td {font-weight: bold; }

[Fang]

Specificity

#table_id td.first_column { width: 100px; font-weight: bold; }

[NotionCommotion]

Thanks Fang!