Move labels after input fields in WooCommerce to make pseudo class possible to create custom checkboxes in CSS. Input fields are placed in labels by default by WooCommerce. We want to make sure the label is placed after the input field so :before pseudo class for +checked labels can be attached to create custom checkboxes in CSS.

woocommerce-move-input-fields-labels-for-pseudo-classes.php

<?php

add_filter( 'woocommerce_form_field_checkbox', 'changeCheckboxFormField', 10, 4 );

 /**
     * Input fields are placed in labels by default by WooCommerce.
     * We want to make sure the label is placed after the input field so :before pseudo class for +checked labels
     * can be attached to create custom checkboxes in CSS. For this to happen within the filter,
     * a part of the function from woocommerce_form_field needs to be copied so we can
     * re-create the Field HTML with the necessary variables and change the order in the $field
     * variable and pass it to $feld_html
     * @see woocommerce_form_field
     */
function changeCheckboxFormField ( $field, $key, $args, $value )
    {
        $custom_attributes         = array();
        $args['custom_attributes'] = array_filter( (array) $args['custom_attributes'], 'strlen' );

        if ( $args['maxlength'] ) {
            $args['custom_attributes']['maxlength'] = absint( $args['maxlength'] );
        }

        if ( ! empty( $args['autocomplete'] ) ) {
            $args['custom_attributes']['autocomplete'] = $args['autocomplete'];
        }

        if ( true === $args['autofocus'] ) {
            $args['custom_attributes']['autofocus'] = 'autofocus';
        }

        if ( $args['description'] ) {
            $args['custom_attributes']['aria-describedby'] = $args['id'] . '-description';
        }

        if ( ! empty( $args['custom_attributes'] ) && is_array( $args['custom_attributes'] ) ) {
            foreach ( $args['custom_attributes'] as $attribute => $attribute_value ) {
                $custom_attributes[] = esc_attr( $attribute ) . '="' . esc_attr( $attribute_value ) . '"';
            }
        }

        if ( $args['required'] ) {
            $args['class'][] = 'validate-required';
            $required        = '&nbsp;<abbr class="required" title="' . esc_attr__( 'required', 'woocommerce' ) . '">*</abbr>';
        } else {
            $required = '&nbsp;<span class="optional">(' . esc_html__( 'optional', 'woocommerce' ) . ')</span>';
        }
        $sort            = $args['priority'] ? $args['priority'] : '';
        $field_container = '<p class="form-row %1$s" id="%2$s" data-priority="' . esc_attr( $sort ) . '">%3$s</p>';
        $label_id        = $args['id'];
        $field_html = '';

        // BOF custom code
        $field = '<input type="' . esc_attr( $args['type'] ) . '" class="input-checkbox ' . esc_attr( implode( ' ', $args['input_class'] ) ) . '" name="' . esc_attr( $key ) . '" id="' . esc_attr( $args['id'] ) . '" value="1" ' . checked( $value, 1, false ) . ' />' .
            '<label class="checkbox ' . implode( ' ', $args['label_class'] ) . '" ' . implode( ' ', $custom_attributes ) . ' for="'.esc_attr( $args['id'] ).'"> ' . $args['label'] . $required . '</label>';
        // EOF custom code

        if ( $args['label'] && 'checkbox' !== $args['type'] ) {
            $field_html .= '<label for="' . esc_attr( $label_id ) . '" class="' . esc_attr( implode( ' ', $args['label_class'] ) ) . '">' . $args['label'] . $required . '</label>';
        }

        $field_html .= '<span class="woocommerce-input-wrapper">' . $field;

        if ( $args['description'] ) {
            $field_html .= '<span class="description" id="' . esc_attr( $args['id'] ) . '-description" aria-hidden="true">' . wp_kses_post( $args['description'] ) . '</span>';
        }

        $field_html .= '</span>';

        $container_class = esc_attr( implode( ' ', $args['class'] ) );
        $container_id    = esc_attr( $args['id'] ) . '_field';
        $field           = sprintf( $field_container, $container_class, $container_id, $field_html );
        return $field;
    }