style.css

.react-phone-number-input__row
{
	/* This is done to stretch the contents of this component */
	display     : flex;
	align-items : center;
}

.react-phone-number-input__phone
{
	/* The phone number input stretches to fill all empty space */
	flex : 1;

	/* The phone number input should shrink
	   to make room for the extension input */
	min-width : 0;
}

.react-phone-number-input__icon
{
	/* The flag icon size is 4x3 hence the exact `width` and `height` values */
	width      : 1.24em;
	height     : 0.93em;

	/* `1px` is still too much for a "retina" screen but there's no way in CSS to specify "hairline" border width. */
	border     : 1px solid rgba(0, 0, 0, 0.5);

	/* Makes sure `width`x`height` is exactly `4x3` and `border` width is not included in it */
	box-sizing : content-box;
}

.react-phone-number-input__icon--international
{
	/* The international icon size is square */
	/* and also has no border hence the `2 * 1px` `width` and `height` compensation */
	width  : calc(0.93em + 2px);
	height : calc(0.93em + 2px);

	/* The international icon size is square hence the exact `padding` value */
	/* for precise alignment with `4x3` sized country flags. */
	padding-left  : 0.155em;
	padding-right : 0.155em;

	border : none;
}

.react-phone-number-input__error
{
	margin-left : calc(1.24em + 2px + 0.3em + 0.35em + 0.5em);
	margin-top  : calc(0.3rem);
	color       : #D30F00;
}

.react-phone-number-input__icon-image
{
	max-width  : 100%;
	max-height : 100%;
}

/* Removes `<input type="number"/>` up/down arrows in Webkit browsers. */
.react-phone-number-input__ext-input::-webkit-inner-spin-button,
.react-phone-number-input__ext-input::-webkit-outer-spin-button
{
	margin             : 0 !important;
	-webkit-appearance : none !important;
	-moz-appearance    : textfield !important;
}

.react-phone-number-input__ext-input
{
	width : 3em;
}

.react-phone-number-input__ext
{
	white-space: nowrap;
}

.react-phone-number-input__ext,
.react-phone-number-input__ext-input
{
	margin-left : 0.5em;
}

/* Styling native country `<select/>`. */

.react-phone-number-input__country--native
{
	position     : relative;
	align-self   : stretch;
	display      : flex;
	align-items  : center;
	margin-right : 0.5em;
}

.react-phone-number-input__country-select
{
	position : absolute;
	top      : 0;
	left     : 0;
	height   : 100%;
	width    : 100%;
	z-index  : 1;
	border   : 0;
	opacity  : 0;
	cursor   : pointer;
}

.react-phone-number-input__country-select-arrow
{
	display            : block;
	content            : '';
	width              : 0;
	height             : 0;
	margin-bottom      : 0.1em;
	margin-top         : 0.3em;
	margin-left        : 0.3em;
	border-width       : 0.35em 0.2em 0 0.2em;
	border-style       : solid;
	border-left-color  : transparent;
	border-right-color : transparent;
	color              : #B8BDC4;
	opacity            : 0.7;
	transition         : color 0.1s;
}

/* Something from stackoverflow. */
.react-phone-number-input__country-select-divider
{
	font-size  : 1px;
	background : black;
}

.react-phone-number-input__country-select:focus + .react-phone-number-input__country-select-arrow
{
	color : #03B2CB;
}

/* Styling phone number input */

.react-phone-number-input__input
{
	height        : calc(0.3rem * 6);
	outline       : none;
	border-radius : 0;
	padding       : 0;
	appearance    : none;
	border        : none;
	border-bottom : 1px solid #C5D2E0;
	transition    : border 0.1s;
	font-size     : inherit;
}

.react-phone-number-input__input:focus
{
	border-color : #03B2CB;
}

.react-phone-number-input__input--disabled
{
	cursor : default;
}

.react-phone-number-input__input--invalid,
.react-phone-number-input__input--invalid:focus
{
	border-color : #EB2010;
}

/* Overrides Chrome autofill yellow background color */
.react-phone-number-input__input:-webkit-autofill
{
	box-shadow : 0 0 0 1000px white inset;
}

/* A small fix for `react-responsive-ui` */
.react-phone-number-input__country .rrui__select__button
{
	border-bottom : none;
}