Example showing how to add custom CSS to the Event Espresso Transactions admin page

espresso_txn.php

<?php
//* Please do NOT include the opening php tag, except of course if you're starting with a blank file

add_action(
    'admin_enqueue_scripts',
    'my_custom_txn_table_column_widths',
     20
);
function my_custom_txn_table_column_widths() {
    $css = 
        '.transactions .column-TXN_ID {
            width: 8% 
        }
        .transactions .column-TXN_timestamp {
            width: 16%;
        }
        .transactions .column-actions {
            width: 16%;
        }';
    wp_add_inline_style('espresso_txn', $css);
}