Wallet NET worth should not be confused with wallet balance.
Wallet NET worth is a sum of all funds held in the wallet, denominated in one currency (you can choose the denomination currency in the dropdown menu).
Wallet net worth does not display your actual wallet balance.
It is subject to change either because of the change in XRP market value or because of the change in market value of one of the other currencies held in the wallet.
Example: If 1 XRP is currently worth 2 USD
Wallet net worth in XRP: 30 XRP + 35 XRP (70 USD if converted to XRP) = 65 XRP
Wallet net worth in USD: 70 USD + 60 USD (30 XRP if converted to USD) = 130 USD