In Office 365 environment, you have to provision everything through CSOM. Content type is basic building blocks of any SharePoint List and Libraries.  Here is the CSOM Code snippet to create a new Content type and Its ID.

ContentTypeCollection contentTypes = web.ContentTypes;
cc.Load(contentTypes);
cc.ExecuteQuery();

foreach (var item in contentTypes)
{
if (item.StringId == “0x0101009189AB5D3D2647B580F011XA2F359FB3”)
return;
}

// Create a Content Type Information
ContentTypeCreationInformation newCt = new ContentTypeCreationInformation();

newCt.Name = “Custom Content Employee”;

newCt.Id = “0x0101009189AB5D3D2647B580F011XA2F359FB3″”;

newCt.Group = “Custom Content Employee Groups”;
// Create the content type
ContentType myContentType = contentTypes.Add(newCt);
cc.ExecuteQuery();

Please read my another blog to know more about delete ContentTypes in Sharepoint 2013/Office 365 using CSOM

Happy SharePointing Folks !! Hope it helps you.