You can also open this Double iFrame in a:

Here is the code:

HTML - Copy this into an HTML block in the page editor:

<div>
    <span style="float:right; width:50%; height:850px">
        <iframe src="https://ghost-o-matic.com"></iframe>
    </span>
    <span style="float:right; width:50%; height:850px">
        <iframe src="https://denvergeeks.com"></iframe>
    </span>
</div>

CSS - In your Site (or Post) Settings >> Code Injection >> Site Header . . .
insert-styles-header-injection

Paste the below code:

<style>
iframe {
box-shadow: -1px 3px 28px -4px rgba(0,0,0,0.76);
float: left;
width: 100%;
height: 800px;
border-top-width: 0px;
border-right-width: 0px;
border-bottom-width: 0px;
border-left-width: 0px;
border-style: inset;
border-color: initial;
border-image: initial;
}
</style>