Ghost/ghost/admin/app/templates/components/modal-post-email-preview.hbs

<header class="modal-header gh-pe-header {{if (eq type "desktop") "gh-pe-header-border"}}" data-test-modal="preview-email" style="display:flex">
    <h2 class="f6 fw6">{{subject}}</h2>
    <div class="gh-contentfilter gh-btn-group gh-pe-btn-group" style="display:flex;flex-grow:1;justify-content:center">
        <button class="gh-btn {{if (eq type "desktop") "gh-btn-group-selected"}}" {{action "changeType" "desktop"}}><span>Desktop</span></button>
        <button class="gh-btn {{if (eq type "mobile") "gh-btn-group-selected"}}" {{action "changeType" "mobile"}}><span>Mobile</span></button>
    </div>
    <div class="gh-pe-close">
        <button class="close" href="" title="Close" {{on "click" this.closeModal}}>
            {{svg-jar "close"}}
        </button>
    </div>
</header>

{{#if (eq type "mobile")}}
    <div class="modal-body modal-preview-email-content gh-pe-mobile-container" style="display: flex;justify-content: center;">
        <div class="gh-pe-mobile-bezel">
            <div class="gh-pe-mobile-screen">
                <iframe class="bn gh-pe-iframe" {{did-insert this.renderEmailPreview}}></iframe>
            </div>
        </div>
    </div>
{{/if}}

{{#if (eq type "desktop")}}
    <div class="modal-body modal-preview-email-content gh-pe-desktop-container">
        <iframe class="bn miw-100 gh-pe-iframe" style="height:100%;" {{did-insert this.renderEmailPreview}}></iframe>
    </div>
{{/if}}