JSFiddle - React, Tailwind, and code Playground

HTML

<div id="wrapper">
    <section id="side-fixed"></section>
    <nav id="nav1">
        <ul>
            <li><a href="">home</a>
            </li>
            <li><a href="">home</a>
            </li>
        </ul>
    </nav>
    <section id="principal">
        <header>
            <article></article>
        </header>
        <section id="main-dos">
            <section class="format-box">
                <ul> <a href="http://www.google.es/"><li>enlaces</li></a>
 <a href=""><li>link</li></a>
 <a href=""><li>link</li></a>
 <a href=""><li>link</li></a>

                </ul>
                <article class="sub-article">Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</article>
               ...

CSS

body {
    background: #FAD6D6;
    font-family: verdana;
    font-size: 0.75em;
}
a {
    text-decoration: none;
}
ul {
    list-style: none;
}
/*-------------------PRINCIPAL-------------------------------------------*/
 #nav1 {
    background: #FFADAD;
    height: 100%;
    width: 15%;
}
#principal {
    height: 100%;
    width: 60%;
}
#wrapper {
    background: pink;
    height: 47.5em;
    margin: 10px auto;
    width: 77.5em;
}
#side-fixed {
    height: 100%;
    width: 25%;
}
#nav1, #principal, #side-fixed {
    float: left;
}
header {
    height: 18%;
}
/*-------------------------------NAVEGADOR PRINCIPAL--------------------*/
 #nav1 li {
    text-align: right;
    font-family: arial;
    font-size: 12.7px;
}
#nav1 ul li a {
    background: #124A63;
    color: #ffffff;
    display: inline-block;
    padding: 0.4em 0.8em 0.4em 1.3em;
    margin: 0.2em 3em 0.3em auto;
}
#nav1 ul li a:hover {
    background: crimson;
    color: #124A63;
}
/*----------------------------------------------dos------------------------------*/
 #main-dos {
    background: #BBCED9;
    height: 82%;
    overflow: hidden;
}
.format-box {
    color: #394A58;
    font-size: 0.96em;
    height: 90%;
    margin: 1.9em auto;
    text-align: justify;
    width: 88%;
    overflow: hidden;
    position: relative;
    z-index: 1;
}
.format-box ul a li {
    background: #ffffff;
    border: 2px solid white;
    float: left;
    font-family: arial;
    font-size: 12px;
    font-weight: bold;
    margin-right: 3.5px;
    padding: 2px;
}
.format-box ul a li:hover {
    background: #124A63;
    color: white;
}
.sub-article {
    height: 50%;
    overflow-y: scroll;
    width: 98%;
}
.sub-photo {
    border: 1px solid black;
    height: 30%;
    width: 80%;
}
#caja-cortina {
    position: absolute;
    left: 575px;
    top: 134px;
    height: 422px;
    width: 490px;
    z-index: 5;
    animation:cortina-bajando 3s;
    -webkit-animation:cortina-bajando 3s;
    -moz-animation:cortina-bajando 3s;
   ...