style.css

@import url('https://fonts.googleapis.com/css?family=Open+Sans&display=swap');

* {
  box-sizing: border-box;
}

:root {
    /* normal (light) colors. */
    --background_color_el: hsl(0, 0%, 100%);
    --body_color: hsl(0, 0%, 90%);
}

/* placeholder text color. */
.search::placeholder {
    color: inherit;
}

body {
    background-color: var(--body_color);
    color:hsl(200, 15%, 8%);
    font-family: 'Open Sans', sans-serif;
    margin: 0;
}

body.dark {
    /* define the dark mode colors. */
    --body_color: hsl(207, 26%, 17%);
    --background_color_el: hsl(209, 23%, 22%);
    /* different bg dark color, to distinguish it better. */
    background-color: hsl(207, 26%, 17%);
    color: white; /* text color. */
}

header {
    background-color: var(--background_color_el);
    padding: 0px;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.25), 0 10px 10px rgba(0, 0, 0, 0.22);
}

header.dark {
    background-color: var(--background_color_el);
}

h1 {
    margin: 0;
}

/* button styling. */
.btn-dark-mode {
    background-color: var(--background_color_el);
    color: inherit;
    font-size: 16px;
    border: none;
    cursor: pointer;
}

.btn-dark-mode:hover {
    filter: brightness(110%);
}

.btn-dark-mode .fas {
    display: none;
}

body.dark .btn-dark-mode .fas {
    display: inline-block;
}

body.dark .btn-dark-mode .far {
    display: none;
}

/* input styling. */
.search {
    background-color: var(--background_color_el);
    color: inherit;
    font-size: 14px;
    padding: 20px;
    border: none;
    border-radius: 4px;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.25), 0 10px 10px rgba(0, 0, 0, 0.22);
    min-width: 300px;
}

.search:hover {
    filter: brightness(110%);
}

/* dropdown styling. */
.dropdown {
    background-color: var(--background_color_el);
    position: relative;
    display: inline-block;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.25), 0 10px 10px rgba(0, 0, 0, 0.22);
    font-size: 14px;
    padding: 20px;
    border-radius: 4px;
    cursor: pointer;
}

.dropdown:hover {
    filter: brightness(110%);
}

.dropdown ul {
    background-color: inherit;
    display: none;
    list-style: none;
    position: absolute;
    top: 55px;
    left: 0;
    width: 100%;
    padding: 2px;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.25), 0 10px 10px rgba(0, 0, 0, 0.22);
    box-decoration-break: inherit;
}

.dropdown.open ul {
    display: block;
    padding-left: 20px;
}

.dropdown ul li {
    margin: 10px 0;
}

.dropdown .fa-chevron-down {
    margin-left: 4px;
}

/* card styling. */
img {
    max-width: 100%;
    max-height: 200px;
}

.container {
    display: flex;
    flex-wrap: wrap;
    max-width: 1440px;
    margin: auto;
    padding: 20px;
    align-items: center;
    justify-content: space-between;
    /* position: relative; */
}

.card {
    width: 300px;
    height: 400px;
    margin: 10px;
    background-color: var(--background_color_el);
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.25), 0 10px 10px rgba(0, 0, 0, 0.22);
    border-radius: 4px;
    overflow: hidden;
    cursor: pointer;
}

.card:hover {
    filter: brightness(110%);
}

.card img {
    object-fit: cover;
    height: 180px;
    width: 100%;
}

.card-header {
    margin: 0;
}

.card-body {
    padding: 20px;
}

.card-body h2 {
    margin: 0;
}

.container.countries {
    justify-content: center;
}

/* modal styling. */
.modal {
    background-color: inherit;
    display: none;
    align-items: center;
    justify-content: center;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    z-index: 100;
}

.container:hover {
    filter: brightness(110%);
}

.modal .container {
    background-color: var(--background-el);
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.06), 0 1px 2px rgba(0, 0, 0, 0.12);
}

.modal img {
    max-width: 300%;
}

.modal-body {
    padding: 30px;
}

.btn-close {
    border: none;
    position: relative;
    top: -200px;
    right: -600px;
    font-size: 20px;
    cursor: pointer;
}

.btn-close:hover {
    filter: brightness(110%);
}