BestSell Shopping Website
Hooks are JavaScript functions, but they impose two additional rules:

Only call Hooks at the top level. Don't call Hooks inside loops, conditions, or nested functions.
Only call Hooks from React function components. Don't call Hooks from regular JavaScript functions. 
1.Build the home page:
    a.header and footer:
        i.header - BestSell title on the left, suitable padding left;
                   cart icon and login link on the right, icon on the left of the login, set up appropriate gap between them;
                   appropriate background for the header.
        ii. footer - text "All right is reserved" on the center of the footer,
                     appropriate background for the footer.
    b.number of products, filter, and dividing line
        i.number of products - count the number of products then present on the
                               left. 
        ii.filter - two drop-down lists used for filtering products are under
                   the header but on the top of dividing line.    
        iii.dividing line - add <hr> under the filter
    c.product
        i. present a list of product on the body with appropriate gap between 
           each product;
           put product name and price at the bottom of each product


Add redux:
    1. what is redux(diagram)
    2. npm install redux
    3. create types
    4. types.js
    5. define FETCH_PRODUCTS
    6. actions/productActions.js
    7. declare fetchProducts
    8. create reducers
    9. reducers/productReducers.js
    10. define case FETCH_PRODUCTS
    11. create store.js