Style Dropdown Select Menus in Chrome – Square Corners and Height - https://amethystwebsitedesign.com/style-dropdown-select-menus-in-chrome-square-corners-and-height

style.css

/* Default theme form styles, similar to Genesis Sample */
input,
select,
textarea {
	background-color: #fff;
	border: 1px solid #ccc;
	color: #545454;
	font-size: 18px;
	font-size: 1.8rem;
	font-weight: 400;
	padding: 12px 16px;
	width: 100%;
}

/* Add for select with square corners and matching height */
select {
	padding: 10px 16px; /* Firefox */

	height: 50px;  /* Chrome & Safari */
	-webkit-border-radius: 0;
	border: 0;
	outline: 1px inset #fff;
	outline-offset: -1px;
}

/*Notes:
The padding can be adjusted for Firefox, if you see the text cut off. 
Just make the top and bottom padding a few pixels smaller than the default styles.
Next is the height declaration; adjust this so the select field matched the height of the other input fields.
The last four lines are what makes the corners square; #fff is the background color in the default CSS.
*/