JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
  <div class="parent-child">
    <div class="parent-child-title">Заголовок</div>
  </div>
  <div class="parent-child main-child">
    <div class="parent-child-title">Большой заголовок</div>
  </div>
  <div class="parent-child">
    <div class="parent-child-title">Заголовок</div>
  </div>
</div>

SCSS

.parent {
  &-child {
    &-title {
      font-size: 20px;
      color: red;
    }

    .main-child & {
      &-title {
        font-size: 40px;
        color: green;
      }
    }
  }
}