Can you edit WP gutenberg block css without a plugin?

Question

I want to add custom css to my gutenberg table block. I want to adjust the css width of the tds. Ive tried selected the "Fixed Width table cells" toggle but the table seems to have different widths. Is there a way to do that because all of the plugins I have used dont seem to work. I tried adjusting the css in the theme.css and style.css files in css/dist/block-library folder. Do I need to compile it and that is why I am not seeing the changes?

in the theme.css folder

.wp-block-table td,
.wp-block-table th {
  padding: 0.5em;
  border: 1px solid;
  word-break: normal;
  width:460px; //this is what i added
}

in the style.css folder

.wp-block-table .has-fixed-layout td,
.wp-block-table .has-fixed-layout th {
  word-break: break-word;
  width:460px; //this
}
.wp-block-table.alignleft td,
.wp-block-table.alignleft th, .wp-block-table.aligncenter td,
.wp-block-table.aligncenter th, .wp-block-table.alignright td,
.wp-block-table.alignright th {
  word-break: break-word;
  width:460px; //this
}
.wp-block-table.is-style-stripes th,
.wp-block-table.is-style-stripes td {
  border-color: transparent;
  width:460px; //this
}

Answer 1

One way to achieve this is to add a button to the Table Block in the editor. You create your Table, select the Table block, then click the button and the custom CSS is applied - then Publish.

Move the code into a file in a new folder and call it from the functions file. Try this example...

Edit: This has a custom colour - you may need to change that to get it working.

/assets/custom.php
    function custom_block_styles() {

        register_block_style( 
            'core/table', 
            array(
                'name' => 'blue-stripes',
                'label' => 'Blue Stripes',
                'inline_style' => '.wp-block-table.is-style-blue-stripes tbody tr:nth-child(2n+1) { background-color: var(--wp--preset--color--pale-blue);}.wp-block-table.is-style-blue-stripes td, .wp-block-table.is-style-blue-stripes th {border-color: transparent;padding: 0 2px;}.wp-block-table.is-style-blue-stripes td:nth-child(n+2) {border-left: 2px solid #eee;}',
            )
        );
    }
    add_action( 'init', 'custom_block_styles' );
    
functions.php
require get_template_directory() . '/assets/custom.php';