Magento 2.1 – How to Fix Deploy Static Content Error

I got this error when running setup:static-content:deploy on Magento 2.1.8:

Compilation from source: /microcloud/domains/vampm2/domains/mydomains.co.uk/http/vendor/magento/theme-frontend-blank/web/css/styles-m.less

Compilation from source:
frontend/Venustheme/cricket_child/en_GB/css/styles-m.less
variable @checkout-step-content-mobile__background is undefined in file /microcloud/domains/vampm2/domains/mydomain.co.uk/http/var/view_preprocessed/css/frontend/Venustheme/cricket_child/en_GB/Magento_Checkout/css/source/module/checkout/_shipping.less in _shipping.less on line 213, column 34
211|         .form-shipping-address,
212|         .methods-shipping {
213|             .lib-css(background, @checkout-step-content-mobile__background);
214|             .lib-css(margin, @checkout-step-content-mobile__margin);
215|             .lib-css(padding, @indent__base @checkout-step-content-mobile__margin-s);
 in _responsive.less

This is a .less file form /vampm2/domains/mydomian.co.uk/http/app/design/frontend/Venustheme/cricket_child/Magento_Checkout/web/css/source/module/checkout/_shipping.less:

.media-width(@extremum, @break) when (@extremum = 'max') and (@break = @screen__s) {
    .opc-wrapper {
        .form-login,
        .form-shipping-address,
        .methods-shipping {
            .lib-css(background, @checkout-step-content-mobile__background);
            .lib-css(margin, @checkout-step-content-mobile__margin);
            .lib-css(padding, @indent__base @checkout-step-content-mobile__margin-s);
        }

UPDATE The variable is not defined within this file. There are variables defined at the top of this page but checkout-step-content-mobile__background is not. From comments below, the checkout-step-content-mobile__background variable is defined in the _checkout.less file and I have found the declaration only in the http\vendor\magento\theme-frontend-luma\Magento_Checkout\web\css\source\module\checkout\_checkout.less but from what the system.log say's, it's trying to pull it from theme-frontend-blank:

[2017-12-14 12:24:08] main.CRITICAL: Compilation from source: /microcloud/domains/vampm2/domains/operationvape.co.uk/http/vendor/magento/theme-frontend-blank/web/css/styles-m.less

UPDATE

Here is the error from my system.log:

[2017-12-14 12:24:08] main.CRITICAL: 
Compilation from source: 
frontend/Venustheme/cricket_child/en_US/css/styles-m.less
variable @checkout-step-content-mobile__background is undefined in file /microcloud/domains/vampm2/domains/operationvape.co.uk/http/var/view_preprocessed/css/frontend/Venustheme/cricket_child/en_US/Magento_Checkout/css/source/module/checkout/_shipping.less in _shipping.less on line 213, column 34
211|         .form-shipping-address,
212|         .methods-shipping {
213|             .lib-css(background, @checkout-step-content-mobile__background);
214|             .lib-css(margin, @checkout-step-content-mobile__margin);
215|             .lib-css(padding, @indent__base @checkout-step-content-mobile__margin-s);
216|         }
 in _responsive.less [] []
[2017-12-14 12:24:08] main.CRITICAL: Compilation from source: /microcloud/domains/vampm2/domains/operationvape.co.uk/http/vendor/magento/theme-frontend-blank/web/css/styles-m.less