file-wrapper.css

/*
 * Wrap file input like this.
 * <span class="file-wrapper">
 *   <span class="class-for-your-custom-button">Choose a Photo</span>
 *   <input type="file" name="photo" id="photo" />
 * </span>
 */
.file-wrapper {
  cursor: pointer;
  overflow: hidden;
  position: relative;
  display: inline-block;
  vertical-align: baseline;
  zoom: 1;
  *display: inline;
  *vertical-align: auto;
}
.file-wrapper input {
  cursor: pointer;
  font-size: 100px;
  height: 100%;
  filter: alpha(opacity=1);
  -moz-opacity: 0.01;
  opacity: 0.01;
  position: absolute;
  right: 0;
  top: 0;
}