Why is there a difference in the price on the dashboard and on the buy/sell screen?
The price on the stock dashboard is the closing price whereas the price on the buy/sell screen is the NBBO quote (the best available price to buy or sell). So, basically, on the dashboard, it shows the latest market data.
Once you go on the buy screen, it shows the NBBO (National Best Bid offer) quote which is a standardized buy/sell quote across the US market.
So for example, Alphabet's $1150.05 is the closing price, whereas $1152.59 is the best price available to buy currently (or in other words the lowest price that a seller is willing to sell currently)