I don’t see any issue with the input field, the lettres show fine in them so you may have a bad setting in your browser. You should test other browsers and computers.
As far as what sets the height of these input boxes, it appears to be managed by Woocommerce style sheet, so you should do the changes there.
In the cart field, the height is done by
.woocommerce form .form-row input.input-text, .woocommerce form .form-row textarea {line-height:1;}
So you could eventually use that rule with a font-size and padding, but it is not a good idea to use weaver Custom CSS Rule box to override a plugin CSS, it is best done using the plugin setting or plugin custom CSS. You should ask Woocommerce what is the best way to set it