The following are some useful references. You can go through it to refresh your HTML & CSS knowledge.
HTML5 Tutorial by MDN Web Docs: HTML5 is a markup language used for structuring and presenting content on the World Wide Web.
CSS 3 Tutorial by MDN Web Docs: CSS3 stands for Cascading Style Sheet level 3, which is the advanced version of CSS. It is used for structuring, styling, and formatting web pages. Several new features have been added to CSS3 and it is supported by all modern web browsers
CSS Grid Garden: Grid Garden is a game for learning CSS grid layout.
Learn CSS Layout: To learn CSS layout you can follow this article.
Learn BEM — Block Element Modifier: BEM is a front-end naming method for organizing and naming CSS classes. The Block, Element, Modifier methodology is a popular naming convention for class names in HTML and CSS. It helps to write clean CSS by following some simple rules