put two fields in the same row

See Styling Contact Form for a general explanation of styling CF7 forms using CSS.

There is a link at the bottom of the page to a comprehensive and detailed article on Styling Contact Form 7 Forms

To “put some fields next to each other” I use Ordered List elements to display multiple fields on single line.

HTML:

<ol class="singleline">
<li> <label for="cf7-phone">Phone</label> [text cf7-phone 15/]</li>
<li> <label for="cf7-mobile">Mobile</label> [text cf7-mobile 15/]</li>
</ol>

Added to Form section of CF7 interface. Labels are added for improved accessability.

CSS:

.wpcf7-form .singleline ol {
list-style: none;
margin: 0;
}

.wpcf7-form .singleline li{
display: inline-block;
float: left;
margin-right: 10px;
padding-right: 10px;
}

Add via Child Theme or use custom CSS plugin.