* {
    box-sizing: border-box;
}
body.dark{
    background-color: #000;
    color: #fff;
}
body.dark img{
    width: 15%;
    max-width: 50%;
    align-content: center;
    
}
footer.dark{
    display: block;
    margin-left: auto;
    margin-right: auto;
}
img {
    width: 10%;
    max-width: 50%;
    align-content: center;
    padding: 1em;
    display: block;
    margin-left: auto;
    margin-right: auto;
}
header{
    text-align: center;
    padding: 50px;
}
.b_title{
    font-size: 50px;
}
.sub{
    font-size: 20px;
    color: #006eb6;
    padding-bottom: 10px;
}
.line_box{
    display: flex; 
    flex-direction: column;
    align-items: center;
    width: 475px; 
    margin: 0 auto; 
}
.line_box::after{
    content: ''; 
    display: block;
    width: 100%; 
    height: 2px; 
    background-color: #ccc; 
}
.upper{
    margin: 10px;
    padding: 1px;
}
.lower{
    margin: 10px;
    padding: 1px;
    text-align: left;
}
main {
    font-size: 15px;
    font-family: 'Times New Roman', Times, serif;
    display: grid;
    place-items: left;
    align-items: auto;
    max-width: 500px;
    margin: 0 auto;
    
}