style.css

:root {
    --txt: #bbb;
    --bkg: #111;
}

* {
    margin: 0;
    padding: 0;
    background-color: var(--bkg);
    color: var(--txt);
    font-family: 'Source Sans Pro', sans-serif;
    user-select:none;
    -ms-user-select: none;
    -webkit-user-select: none;
    -moz-user-select: none;
}

.age {
    width: 100vw;
    margin-top: 15vh;
    text-align: left;
    cursor: default;
    font-weight: bold;
}

.age .title {
    font-size: 10vmin;
    padding: 5vmin 0 0 0;
}
.age input {
    font-size: 5vmin;
    padding: 10px;
    margin: 15px 0;
    border-radius: 10px;
    border: 0.4vmin solid var(--txt);
    width: 67vmin;
    font-family: monospace;
}
#birthdate {
    width: 42vmin;
}

#birthtime {
    width: 22vmin;
}

.button { 
    font-size: 5vmin;
    padding: 2vmin;
    margin: 2.5vmin;
    width: 30vmin;
    border-radius: 10px;
    border: 0.4vmin solid var(--txt);
    cursor: pointer;
}

.age .time {
    font-size: 6vmin;
    margin: 10px 0;
}

.container {
    display: flex;
    justify-content: space-around;
    flex-wrap: wrap;
}

.block {
    margin: 20px;
    text-align: left;
    /* border: 1px solid var(--txt); */
    /* width: 70vmin; */
}