BEM (Block Element Modifier) naming system for CSS

• BEM — is a methodology that helps you to create reusable components and code sharing in front‑end development

And other methodology options

• OOCSS — Separating container and content with CSS “objects”
• SMACSS — Style-guide to write your CSS with five categories for CSS rules
• SUITCSS — Structured class names and meaningful hyphens
• Atomic — Breaking down styles into atomic, or indivisible, pieces