JSFiddle - React, Tailwind, and code Playground

HTML

<header class="header">

  <div class="header__inner">
    <div class="header__social">
      социалки
      <ul class="social">
        <li><a class="social__link" href="">1</a></li>
        <li><a class="social__link" href="">2</a></li>
        <li><a class="social__link" href="">3</a></li>
        <li><a class="social__link" href="">4</a></li>
      </ul>
    </div>
    <form class="header__subscribe">
      <label for="email"></label>
      <input class="email" type="search" name="" id="email">
      <button class="btn" type="submit">btn</button>
    </form>
  </div>

</header>

CSS

@import url('https://fonts.googleapis.com/css2?family=Neucha&display=swap');


* {
  box-sizing: inherit;
}

html {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: 'Neucha', cursive;
  color: #eee;
}

.header {
  background: #1d263a;
}

.header__inner {
  display: flex;
  max-width: 800px;
  /* поменяйте на ширину контентной области макета */
  margin: 0 auto;
}

.header__social {
  display: flex;
  align-items: center;
  width: 50%;
  padding: 8px 0;
}

.social {
  display: flex;
  width: 50%;
  margin: 0 0 0 1em;
  padding: 0;
  list-style-type: none;
}

.social__link {
  display: block;
  padding: 10px 16px;
  margin: 0 3px;
  border-radius: 4px;
  color: #f00;
  background: #eee5;
  text-decoration: none;
}

.header__subscribe {
  display: flex;
  width: 50%;
  padding: 8px 0 8px 20px;
  border-left: 1px solid #eee5;
}
.email {
  flex: 1;
  border: 0;
}
.btn {
  padding: 0.3em 1em;
  border: 0;
  background: #900;
  color: #fff;
  font: inherit;
  
}