html - Targetting a specific Mobile page in wordpress back end -

im trying change ground specific post on mobile wordpress page.

@media screen , (max-width: 940px) #page { max-width: 768px; width: 100%;  margin: 0 auto;   background: #007a52; box-shadow: 0 0 10px #999; } 

i know page id used im not sure how?

http://www.thedoughbros.ie/wp-content/plugins/contact-form-7/includes/css/styles.css

the file above has following css , custom backgrounds posts.

806 represents post-id if want custom backgrounds keep adding new blocks different id

@media screen , (max-width: 940px) page.custom-background.page-id-806   /*-------------------------------------------------------------- custom backgrounds --------------------------------------------------------------*/ body.custom-background.page-id-806  {  background-image: url( http://www.thedoughbros.ie/wp-content/uploads/2015/05/menubackground.fw_.png);    }  body.custom-background.page-id-723  {  background-image: url(http://thedoughbros.ie/wp-content/uploads/2015/03/van3.fw_.png);     }  body.custom-background.page-id-822  {  background-image: url(http://thedoughbros.ie/wp-content/uploads/2015/03/restaurant3.fw_.png);     }   @media screen , (max-width: 940px) page.custom-background.page-id-806   {  background: #fff !important;     }      body.custom-background.page-id-346  {  background-image: url(http://thedoughbros.ie/wp-content/uploads/2015/06/14jun.fw_.png);    } 

just add new blocks of css

@media screen , (max-width: 940px) page.custom-background.page-id-807   {  background: #fff !important;     }  @media screen , (max-width: 940px) page.custom-background.page-id-808   {  background: #fff !important;     }  @media screen , (max-width: 940px) page.custom-background.page-id-809   {  background: #fff !important;     } 

or multiple

@media screen , (max-width: 940px) page.custom-background.page-id-807, page.custom-background.page-id-808, page.custom-background.page-id-809, page.custom-background.page-id-810   {  background: #fff !important;     }