Regions on appearing properly

So I was looking at the region definition of my theme and I found that the regions are not appearing properly. For instance, the sidebar is not displaying on the left side of the page; but instead it is displaying just below my content region. Below is a snippet of my page.html.twig file.

<div id="page-wrapper">
  <div id="page">
    <header id="header" class="header" role='banner'>
      <div class="layout-header">
        {{ page.header }}
      </div>
    </header>

    {% if page.search %}
      <div class="search">
        <aside class="layout-search" role="complementary">
          {{ page.search }}
        </aside>
      </div>
    {% endif %}

    <div id="main-wrapper" class="layout-main-wrapper">
      <div id="main" class="layout-main">
        <main id="content" class="layout-content" role="main">
          <section class="section">
            <a id="main-content" tabindex="-1"></a>
            {{ page.content }}
          </section>
        </main>
        {% if page.sidebar_first %}
          <div id="sidebar-first" class="layout-sidebar-first">
            <aside class="section" role="complementary">
              {{ page.sidebar_first }}
            </aside>
          </div>
        {% endif %}
      </div>
    </div>
  </div>
</div>

I hope you could help me with this error.