The size is specified in your theme's CSS stylesheet.
http://librairieduforez.fr/wp-content/themes/spritz/css/bootstrap.min.css?ver=1.0
Line #229
input, textarea, .uneditable-input {
width: 206px;
}↧
Takayuki Miyoshi on "[Plugin: Contact Form 7] Textarea width impossible to change"
↧