Кристина

<div class="container">
  <section class="news">
    <div class="news__item">Новость</div>
    <div class="news__item">Новость</div>
    <div class="news__item">Новость</div>
    <div class="news__item">Новость</div>
    <div class="news__item">Новость</div>
  </section>
  <aside class="sideBar">Боковое меню</aside>
</div>

.container{
  display: flex;
  max-width: 1200px;
  background: #eee;
  margin: 0 auto;
}

.news{
  display: flex;
  flex-wrap: wrap;
  flex-grow: 1;
  background: lightgreen;
}

.news__item{
  flex-basis: 200px;
  flex-grow: 1;
  height: 300px;
  margin: 10px;
  background: lightblue;
}

.sideBar{
  flex-grow: 1;
  max-width: 400px;
}