JSFiddle - React, Tailwind, and code Playground

HTML

<div class="header">
  <div class="header__item">
    Текст
  </div>
  <div class="header__item">
    Текст
  </div>
</div>

CSS

.header {
  height: 50px;
  width: 100%;
  background-color: #263448;
  padding-left: 15px;
  overflow: hidden;
}

.header__item {
  position: relative;
  height: 50px;
  display: inline-block;
  line-height: 50px;
  color: #fff;
  margin-right: 15px;
  cursor: pointer;
}

.header__item:after {
  content: " ";
  position: absolute;
  top: 0;
  display: block;
  width: 100%;
  height: 20px;
  margin-top: 50px;
  opacity: 0;
  box-shadow: 0 0 0px 0px #18616f;
  transition: all 0.2s;
}

.header__item:hover:after {
  content: " ";
  opacity: 1;
  box-shadow: 0 0 50px 10px #18616f;
}