*,
*::before,
*::after{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

#main{
    width: min(85%, 700px);
    margin: 30px auto;
}
#main > h1{
    margin-top: 5px;
    margin-bottom: 10px;
}
#how_to_use > h2{
    margin-top: 10px;
    margin-bottom: 10px;
}
#how_to_use > p{
    margin-top: 20px;
    margin-bottom: 20px;
}
#how_to_use h4{
    margin-bottom: 15px;
}

#how_to_use{
    border: 1px solid #000000;
    padding: 10px;
    width: auto;
    background-color: #f8f8f8;
}

table{
    border-collapse: collapse;
    margin-top: 50px;
}

th, td{
    padding: 5px;
}

a,
a:visited{
    color: #0000ff;
    font-weight: bold;
    text-decoration: none;
}
.page_back:hover{
    text-decoration: underline;
}

video {
    width: min(90%, 650px);
}