Hello,
Change 0.9em to 12px below:
Template.CSS - Line 136
.inputbox, .btn, .registration input, .login input, .contact-form input, #jform_contact_message, input, textarea, .validate, button, select, textarea, input[type="text"], input[type="password"], input[type="datetime"], input[type="datetime-local"], input[type="date"], input[type="month"], input[type="time"], input[type="week"], input[type="number"], input[type="email"], input[type="url"], input[type="search"], input[type="tel"], input[type="color"], .uneditable-input {
background: #ffffff none repeat scroll 0 0;
border: 1px solid #dadada;
color: #626262;
font-size: 0.9em;
font-weight: 300;
height: auto;
line-height: 1;
padding: 14px 15px 13px;
}