It is nearly impossible to ensure that HTML input file elements match the appearance of other parts of web applications. Browsers offer limited possibilities for styling them, if any at all. However, in newer browser versions, there are some tricks that can help alleviate this common styling problem, and one such method for styling input file elements is explained here.
This solution utilizes HTML/CSS and JavaScript, with a focus on the position:relative, opacity, and z-index features of CSS. It positions normally styled input and image elements so that they overlap precisely with the input file element. The opacity of the input file is set to 0, and its z-index is set to 2, allowing it to lie on top of the normally styled input and image elements while remaining invisible. Additionally, it remains fully clickable to the user.
We have already implemented this clever trick in our JSF-based web application, making slight adjustments to tailor it to our current styling requirements. The end result was highly satisfying for our customers.