부트스트랩 컴포넌트4.0 (예쁜 CSS 모음집)
https://getbootstrap.com/docs/4.0/components/alerts/
구글폰트(한글)
https://fonts.google.com/?subset=korean
HTML은 뼈대, CSS는 꾸미기
자주쓰이는 CSS
h1, h5, background-image, background-size, background-position
color, width, height, border-radius, margin, padding