Field size not working

The overall size of the form elements is generally controlled by the CSS in your current WordPress theme rather than the “size” you use in the Form section of the CF7. This refers to the standard HTML size attribute which may or may not control overall element size.

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. The article shows people, with suitable HTML & CSS skills, how to change the appearance of their Contact Form 7 Forms to meet their particular requirements.

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>

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;
}

Added to Child Theme style.css