Magento 2 common css variables not applied for third party modules

Question

I am using a custom theme, declared common variables under,

app\design\frontend\Zero\my_theme\web\css\source\components

1) _variables.less

Eg:

@h1__font-size: 48px !important;

2) common.less

Eg:

h1 {
    font-size:@h1__font-size !important; 
}

I am using magefan extension, if i use @h1__font-size in blog pages, its not working its returns @h1__font-size variable is undefined, how to solve this error.