Scrape Web data value


I want to scrape a value from a web site, but I can’t.
That’s the code:

  - platform: scrape
    name: "Average MH/s"
    resource: ""
    select: "#app > main > div > div.miner-content > div > div:nth-child(2) > div.dashboard-overview > div.charts > div.hashrate > div > div:nth-child(3) > div > div.stat-card-body > span:nth-child(1)"
    unit_of_measurement: "MH/s"

But does not work, the value of the sensor it is “unknown”

Can anyone help me with that? Thanks!