Using the CSS language only the position and exterior of the Iframe element can be stylized.
The internal content of the Iframe element can not be styled with CSS, this is possible using the JAVASCRIPT language.

Example external CSS style of the Iframe element

<iframe class="frame" src="https://itpresent.com" scrolling="no"></iframe>

<style >
.frame {
width:560px;
height:410px;
border:5px groove red;
border-radius:25px;
}
</style>
result:



JSFiddle





Example CSS position of the Iframe element

In the CSS language, it is possible to specify the position of the Iframe element itself. It is also possible to set the position of the specific HTML content of the document being displayed

<div id="outerdiv">
    <iframe id="frame" src="https://itpresent.com" scrolling="no"></iframe>
</div>

<style >
#outerdiv {
width:580px;
height:130px;
overflow:hidden;
position:relative;
border:5px solid red;
}

#frame {
position:absolute;
top:-280px;
left:-2px;
width:580px;
height:750px;
}
</style>

result:

CodePen