:root {
    --heading-font: "PT Sans", sans-serif;
    --body-font: "Source Sans 3", sans-serif;
    --white: #fff;
    --black: #000;
    --border-bottom-color: #181d1e;
    --text-color-1: hsla(0, 0%, 100%, 0.7);
}

* {
    box-sizing: border-box;
}

html {
    font-size: 62.5%;
}

body {
    font-size: 1.5rem;
    font-family: var(--body-font);
    background-color: #ccc;
}

h1,
h2,
h3,
h4,
h5,
h6 {
    font-weight: 700;
    font-family: var(--heading-font);
}

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

button {
    border: none;
    background-color: transparent;
    cursor: pointer;
}

h1 {
    margin-top: 32px;
    font-size: 2rem;
    text-align: center;
    margin-bottom: 32px;
}

.main-chapter {
    width: 800px;
    margin: 0 auto;
}

.chapter-list {
    width: 340px;
    margin: 0 auto;
    color: #eaeaeb;
    background-color: #272a31;
}

.search-container {
    position: relative;
    padding: 16px;
}

.search-form {
    display: flex;
    width: 80%;
    align-items: center;
    background-color: #323c4a;
    border-radius: 8px;
    padding: 0px 16px;
}

.search-form input {
    width: 100%;
    height: 40px;
    padding-left: 10px;
    font-size: 1.4rem;
    color: var(--text-color-1);
    background-color: transparent;
    border: none;
    outline: none;
}

.search-container span {
    position: absolute;
    top: 50%;
    right: 24px;
    transform: translateY(-50%);
    font-size: 1.6em;
    z-index: 1;
}

.search-container a {
    color: rgb(0, 147, 252);
}

.chapter-list h2 {
    position: sticky;
    top: 0;
    padding: 16px 40px 16px 16px;
    color: var(--white);
    font-size: 1.8rem;
    border-bottom: 1px solid var(--border-bottom-color);
    background-color: #272a31;
    z-index: 1;
}

.chapter-list h2 i {
    position: absolute;
    top: 50%;
    right: 16px;
    transform: translateY(-50%);
    color: var(--white);
}

.chapter-list .lesson-list {
    text-transform: capitalize;
}

.lesson-list li {
    padding: 16px 32px;
    line-height: 1.6;
    opacity: 0.6;
    border-bottom: 1px solid var(--border-bottom-color);
}