html - What is this css structure called?

Question

I am working on my first web dev project, with someone, and I am responsible for the front-end part. In my personal projects I've been using plain css, but in this template I have seen that they are using something else, a different structure, I think. I kind of figure it out how it works, but because I never crossed paths with it before, it makes developing hard for me. I would like to know what it is so I can read some documentation and understand it better. (as an example: usually ,when I use className, I put the class name between "", but here is like css.something) Can you tell me what it is ? I will leave a snippet here

.menuItem {
  @apply --marketplaceListingAttributeFontStyles;
  color: var(--matterColor);
  /* Layout */
  position: relative;
  min-width: 300px;
  margin: 0;
  padding: 4px 30px;
  display: flex;
  align-items: center;
  justify-content: center;
  /* Override button styles */
  outline: none;
  text-align: left;
  border: none;
  white-space: nowrap;
  cursor: pointer;
  &:focus,
  &:hover {
    color: var(--matterColorDark);
  }
  &:hover .menuItemBorder {
    width: 6px;
  }
}

<button className={css.menuItem} onClick={()=> this.selectOption(queryParamName, option.key, dates)}>

Answer 1

This is CSS Modules and you can read more about this usage of CSS in these 2 links:

• link1

• link2