* {
    box-sizing: border-box;
}

h1,
h2,
h3,
h4,
h5,
h6 {
    font-weight: bold;
}

h1 {
    font-size: 32px;
}

h2 {
    font-size: 20px;
}

h3 {
    font-size: 18px;
}

p {
    font-size: 16px;
}

b,
strong {
    font-weight: bold;
}

i,
em {
    font-style: italic;
}

u {
    text-decoration: underline;
}

li {
    list-style-type: disc;
}

input,
button,
textarea,
select {
    font-size: inherit;
    font-family: inherit;
}

body {
    /* background-color: rgb(198, 193, 196); */
    font-family:
        system-ui,
        -apple-system,
        BlinkMacSystemFont,
        "Segoe UI",
        Roboto,
        Oxygen,
        Ubuntu,
        Cantarell,
        "Open Sans",
        "Helvetica Neue",
        sans-serif;
    line-height: 1.6;
}

.mt_12 {
    margin-top: 12px;
}

.mt-8 {
    margin-top: 8px;
}

.fw_600 {
    font-weight: 600;
}

html {
    font-size: 16px;
}

/* Bai_1 */

.menu {
    background-color: #3e5cca;
    padding: 20px 60px;
    font-size: 0;
}

.menu li {
    display: inline-block;
    height: 26px;
    margin-top: -2px;
}

.menu > li > a {
    color: white;
    text-decoration: none;
    padding: 20px 20px;
    font-size: 1.125rem;
    margin-bottom: 8px;
    border-left: 2px solid black;
}

.menu > li:first-child > a {
    border-left: none;
}

.menu .active:hover {
    color: black;
    background-color: white;
}

.menu .active:active {
    color: red;
    background: black;
}

.menu li a::before {
    content: "\25B6";
    padding: 0 10px 0 0px;
    height: 0px;
    vertical-align: top;
}

/* Bài 2 */
.heading-1 {
    text-align: center;
    margin-bottom: 32px;
}

.form {
    background: rgb(197, 191, 191);
    max-width: 400px;
    margin: 8px auto;
    border-radius: 16px;
}

.form .form-group {
    margin: 6px auto;
    padding-left: 60px;
    padding-right: 60px;
}

.form-group > label {
    display: block;
}

.form-group .avatar {
    width: 80px;
    height: 80px;
    border-radius: 50%;
    cursor: pointer;
}

.form-group > input,
button {
    outline: none;
    padding: 4px 8px;
    border-radius: 8px;
    border: 2px solid gray;
    width: 100%;
}

.form-group .btn {
    background: #0866ff;
    margin-bottom: 16px;
    border: none;
    color: #ffffff;
    cursor: pointer;
}

.form-group .btn:hover {
    opacity: 0.8;
}
.form-group .btn:active {
    color: #ccc;
    background: white;
}
.form-group input:focus {
    border-color: #07c4ea;
}

.form-group input:user-invalid {
    border-color: red;
}

.form-group:has(input:required)::after {
    content: "*";
    color: red;
    margin: -20px;
}

.form:has(input:focus) {
    border: 2px solid rgb(13, 155, 222);
}

/* Bài 3 */
.container {
    width: 1200px;
    height: 100vh;
    background: white;
    margin: 0 auto;
}
.container .box {
    background: #f7f7f7;
    height: 560px;
    width: 320px;
    display: inline-block;
    vertical-align: top;
    margin: 140px 0 0 40px;
    border-radius: 12px;
}

.container .box:hover {
    cursor: pointer;
    box-shadow: 0 0 20px 14px rgba(0, 0, 0, 0.1);
}

.container .box:nth-child(2) {
    border: 2px solid #23db76;
}

.content > h3,
p {
    padding-left: 16px;
}

.content > h3 {
    padding-top: 14px;
    font-size: 2rem;
}

.content > .btn-current {
    width: 100%;
    margin-bottom: 12px;
    background: #ccc;
    opacity: 0.5;
    border: none;
    padding: 4px;
}
.content .btn-current,
.btn-up {
    width: 80%;
    margin-left: 32px;
}

.content > p {
    font-size: 0.875rem;
}

.content .tick {
    font-size: 0.875rem;
    margin-top: 12px;
}

.content h3:nth-of-type(2)::before {
    content: "$";
    font-size: 1rem;
}

.content .tick::before {
    content: "✓ ";
    color: white;
    display: inline-flex;
    background: #4e9e61;
    border-radius: 50%;
    justify-content: center;
    align-items: center;
    width: 20px;
    height: 20px;
    margin-right: 4px;
}

.content > .btn-up {
    border: none;
    background-color: #4c9c62;
    color: white;
    padding: 4px;
}

.content .discount::after {
    content: "199.99";
    padding-left: 12px;
    opacity: 0.3;
    font-weight: 300;
    text-decoration: line-through;
}

.content .price + p {
    opacity: 0.4;
}

.box-3 .content .tick {
    font-size: 0.875rem;
}

/* Bài 4 */

.main-blog {
    width: 1200px;
    height: 100vh;
    margin: 18px auto;
}

.main-blog .title {
    text-align: center;
}

.main-blog img {
    width: 86%;
    margin: 20px auto;
    border-radius: 12px;
    display: block;
}

.content-body .first-para::first-letter {
    font-size: 3rem;
    font-weight: bold;
    float: left;
    line-height: 0.4;
    margin-right: 4px;
}

.content-body p::first-line {
    font-weight: 500;
}

.content-body p::selection {
    background: #098dd3;
}

.content-body .cool-quote {
    margin: 12px 30px;
    font-style: italic;
}

.content-body .cool-quote::before {
    content: "❝";
}

.content-body .cool-quote::after {
    content: "❞";
}

.main-blog .sub-heading:not(h1) {
    font-weight: 600;
    color: red;
}

.comments {
    height: 50%;
}

.comments .comment-item img {
    width: 40px;
    height: 40px;
    border-radius: 50%;
    float: left;
    margin: 6px 8px 0 0;
}

.comments .comment-item {
    background: #f1eeee;
    margin-top: 18px;
    padding: 12px 12px;
    border-radius: 12px;
}

.comments .comment-item:last-child {
    margin-bottom: 30px;
}

.comments .comment-item:hover {
    cursor: pointer;
    box-shadow: 0 0 20px 14px rgba(0, 0, 0, 0.1);
}

.content-body p:nth-of-type(2)::selection {
    color: blue;
    background: #ccc;
}