Вы можете добавить класс justify-content-center в приведенный ниже div.it будет работать.
Вы должны определить правильный контейнер для этого.
<div class="view-content row justify-content-center">...</div>
.row {
display: flex;
flex-wrap: wrap;
margin-right: 15px;
margin-left: 15px;
}
.col {
flex-basis: 0;
flex-grow: 1;
max-width: 100%;
}
.col-auto {
flex: 0 0 auto;
width: auto;
max-width: none;
}
.content {
font-size: 16px;
font-family: 'Philosopher', sans-serif;
font-weight: normal;
font-style: normal;
color: #adb5bd;
}
.node--view-mode-teaser {
border-bottom: 1px solid #d3d7d9;
margin-bottom: 30px;
padding-bottom: 15px;
}
article, aside, figcaption, figure, footer, header, hgroup, main, nav, section {
display: block;
}
.field--type-video-embed-field {
max-width: 600px;
max-height: 500px;
}
.justify-content-center {
justify-content: center !important;
}
<header>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css" integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh" crossorigin="anonymous">
<header>
<div class="row row-offcanvas row-offcanvas-left clearfix">
<main class="main-content col" id="content" role="main">
<section class="section">
<a id="main-content" tabindex="-1"></a>
<div data-drupal-messages-fallback class="hidden"></div>
<div id="block-gp-page-title" class="block block-core block-page-title-block">
<div class="content">
<h2 class="title text-center mt-4 mb-4">Video</h2>
</div>
</div>
<div id="block-gp-content" class="block block-system block-system-main-block">
<div class="content">
<div class="views-element-container col-auto">
<div class="view view-video view-id-video view-display-id-page_1 js-view-dom-id-4e20251f96bb713d45e0e3a547b7a6680520977f1b90eae104916b0a1f3e4163">
<div class="view-content row justify-content-center">
<div class="views-row">
<article data-history-node-id="6" role="article" about="/ru/node/6" class="node ml-2 mr-2 node--type-video node--promoted node--view-mode-teaser clearfix">
<header>
<h2 class="node__title text-center">
<a href="#" rel="bookmark">
<span class="field field--name-title field--type-string field--label-hidden">Test</span>
</a>
</h2>
</header>
<div class="node__content clearfix">
<div class="field field--name-field-youtube-video field--type-video-embed-field field--label-hidden justify-content-center align-content-center field__item mx-auto">
<div class="video-embed-field-provider-youtube col-auto mx-auto">
<iframe width="340" height="220" frameborder="0" allowfullscreen="allowfullscreen" src="https://www.youtube.com/embed/tgbNymZ7vqY"></iframe>
</div>
</div>
</div>
</article>
</div>
</div>
</div>
</div>
</div>
</div>
</section>
</main>
</div>