This seems to be a common issue with some templates.
This is the generic fix that I've suggested previously to others. Add it to the Custom CSS box in [Event Booking -> Configuration -> Custom CSS tab]. If it doesn't fix your problem, please post a link to a sample page on your site and I can provide you with a customized CSS rule.
Code:
.eb-container textarea, .eb-container input[type="text"], .eb-container input[type="datetime"], .eb-container input[type="datetime-local"], .eb-container input[type="date"], .eb-container input[type="month"], .eb-container input[type="time"], .eb-container input[type="week"], .eb-container input[type="number"], .eb-container input[type="email"], .eb-container input[type="url"], .eb-container input[type="search"], .eb-container input[type="tel"], .eb-container input[type="color"], .eb-container .uneditable-input {
box-sizing: content-box !important;
}
