Google DevTools

Source: https://www.youtube.com/watch?v=x4q86IjJFag

Elements: select elements using top left small arrow, toggle device view, change content/style, hide content, u can see the css file & line #,

Copy element to another location or click n drag....

Color picker to choose colors. up&down arrow to change values or scroll...

Add new styles using + & see color names...

Computed section: box model

Console: alerts(1); 1+3 clear the console select h1 & type $0