*{
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}
html {
    font-size: 16px;
}
body{
    padding-top:50px;
}
body, html {
    margin: 0;
    padding: 0;
    width: 100%;
    min-height: 100vh;
    overflow: hidden;
    font-size: 16px;
}

@media screen and (min-width: 768px) and (max-width: 1919px) {
    html {
        font-size: calc(16px + (24 - 16) * ((100vw - 768px) / (1920 - 768)));
    }
}

@media screen and (min-width: 1920px) {
    html {
        font-size: 24px;
    }
}
#background-video {
    position: fixed;
    top: -50px;
    left: 0;
    width: 100%;
    height: 100%;
    padding:10px 0 ;
    object-fit: cover;
    z-index: -1;
}

#ai-character {
    position: fixed;
    bottom: -60px;
    left: 50%;
    transform: translateX(-50%);
    z-index: 1;
    width:200%;
    max-width:1000px;
}
h1{
    text-align: center;
    font-size: 2.5rem;
}
h1 span{
    font-size: 4.0rem;
}

#birthday_select{
    width:70%;
    max-width:550px;
    text-align: center;
    font-size: 2rem;
    margin:0 auto 10px;
    border: solid 2px #000;
    border-radius: 10px;
    background-color: #fff;
    position: relative;
    z-index: 2;
}
#birthday_select label{
    display: block;
    font-size: 1.3rem;
}
#birthday_select .input-group{
    padding: 5px 0 10px 0;
}
#gender_select{
    width:70%;
    max-width:550px;
    text-align: center;
    font-size: 2rem;
    margin:0 auto;
    border: solid 2px #000;
    border-radius: 10px;
    background-color: #fff;
    position: relative;
    z-index: 2;
}
#gender_select .radio-group{
    padding: 20px 0;
}
#start_btn {
    width:210px;
    height:210px;
    max-width:550px;
    text-align: center;
    font-size: 2.5rem;
    font-weight: bold;
    margin:0 auto 10px;
    border-radius: 100px;
    background-color: rgba(255,255,255,0.5);
    position: absolute;
    bottom: 70px;
    left: 49%;
    transform: translateX(-50%) scale(0.8);
    z-index: 3;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.6s ease-in-out;
    cursor: pointer;
    box-shadow: 0 0 40px rgba(255, 255, 255, 0.5);
    opacity: 0;
    visibility: hidden;
}

#start_btn.show {
    opacity: 1;
    visibility: visible;
    transform: translateX(-50%) scale(1);
}

#start_btn:hover {
    transform: translateX(-50%) scale(1.5);
    text-shadow: 0 0 40px rgba(249, 255, 0, 0.8),
    0 0 40px rgba(249, 255, 0, 0.8),
    0 0 40px rgba(249, 255, 0, 0.8);
}
#message{
    width:100%;
    color:#fff;
    letter-spacing: 0.1em;
    text-shadow:
            -2px -2px 0 #000,
            2px -2px 0 #000,
            -2px 2px 0 #000,
            2px 2px 0 #000;
    text-align: center;
    font-weight: bold;
    font-size: 2rem;
    margin:0 auto;
    position:absolute;
    bottom:10px;
    z-index: 2;
}
input[type="radio"] {
    transform: scale(1.5);
}
input[type="date"] {
    transform: scale(2.0);
}