Project: mobx
Task (moderate): 1) Add appealing Form with label (label[htmlFor="title"], label[htmlFor="detail"]) in BlogForm to input title and detail; BlogForm can be submitted by button (.submit-btn); 
2) When submitted, append this Blog to BlogList, and set this Blog as selected.
3) Use MobX actions to append form data to blogs. 
4) Check title duplication when submit clicked. When title is duplicated, stop submitting and show a red border around the input field.
5) Add a span(.blog-list-len) near 'Hello Blog' in Header.tsx to show the length of blogs