Validate frontend

[PhuocOng]

• Fix the frontend css so it's become responsive height for all components inside
• Add min = 0 to each input so they cannot have negative value
• Set up input so it's only accept integer (start time, end time and customize)
• add validation for input, set up FetchYoutubeData script and Refine format of many file (mainly indenttion)
• Set up .env, reformat for code