How to change search box layout

Hi there,

try adding this CSS:

.search-form input[type="search"],
.search-form button.search-submit {
    border: 0;    
    background-color: transparent;
    color: var(--contrast);
}
.search-form {
    background-color: var(--base-2);
    border-radius: 25px;
    overflow: hidden;
}

You need to revert the search modal to legacy search by this PHP code:

add_filter( 'option_generate_settings', function( $settings ) {
    $settings['nav_search'] = 'enable';

    return $settings;
} );

Adding PHP: https://docs.generatepress.com/article/adding-php/