Disable CKEditor
Disable CKEditor editor and select Full HTML as input format.
But we recommend to create and use a new text input format like Full HTML but without CKEditor editor as explained here: Create a new Text Format without CKEditor in Drupal 8
Full
Use below sample code for full width or single column.
<div class="row">
-- your content --
</div><div class="section">
-- your content --
</div>Two Column
Use below sample code for two column.
<div class="full">
<div class="item">
-- content in first column --
</div>
<div class="item">
-- content in second column --
</div>
</div>Three Column
Use below sample code for three column.
<div class="full">
<div class="item">
-- content in first column --
</div>
<div class="item">
-- content in second column --
</div>
<div class="item">
-- content in third column --
</div>
</div>Four Column
Use below sample code for four column.
<div class="full">
<div class="item">
-- content in first column --
</div>
<div class="item">
-- content in second column --
</div>
<div class="item">
-- content in third column --
</div>
<div class="item">
-- content in fourth column --
</div>
</div>