SF_14.4 - https://www.progress.com/documentation/sitefinity-cms/add-custom-widgets-to-message-templates

grid-9+3-newsletter.html

<div class="sf_cols" data-sf-element="Row">
    <div class="sf_colsOut sf_2cols_1_75">
        <!-- Set styles of the sf_colsIn elements -->
        <div class="sf_colsIn sf_2cols_1in_75" data-sf-element="Column 1">
            
        </div>
    </div>
    <div class="sf_colsOut sf_2cols_2_25">
        <div class="sf_colsIn sf_2cols_2in_25" data-sf-element="Column 2">
        </div>
    </div>
</div>