* {
    box-sizing: border-box;
}

*:focus, input:focus + label {
    outline: none;
    box-shadow: inset 0 0 0 5px lightBlue;
}

body {
    padding: 30px 20px;
    background: #fff;
    color: #333;
}

main {
    max-width: 801px;
    margin: auto;
}

h1 {
    text-align: center;
    margin-top: 0;
}

h2 {
    margin: 0 0 12px;
    font-size: 30px;
}

p {
    margin: 0 0 20px;
    font-size: 20px;
    line-height: 1.5;
}

.tabs {
    display: flex;
    flex-wrap: wrap;
    margin: 0 auto 20px;
    border-radius: 10px 10px 0 0;
}

.radiotab {
    position: absolute;
    opacity: 0;
}

.label {
    width: 100%;
    padding: 22px 20px;
    background: #e5e5e5;
    cursor: pointer;
    font-weight: bold;
    font-size: 23px;
    color: #7f7f7f;
    transition: background .3s, color .3s;
    border: none;
    border-radius: 0;
    text-align: center;
}

.label:hover {
    background: #d8d8d8;
}

.label:active {
    background: #ccc;  
}

.radiotab:checked + .label {
    background: #fff;
    color: #000;
    border-top: solid 2px #000;
    border-left: solid 2px #000;
    border-right: solid 2px #000;
    border-bottom: none;
}

.panel {
    display: none;
    padding: 20px 30px 30px;
    background: #fff;
    width: 100%;
    border-left: solid 2px #000;
    border-bottom: solid 2px #000;
    border-right: solid 2px #000;
}

.radiotab:checked + .label + .panel {
    display: block;
}

@media (min-width: 600px) {
    .panel {
        order: 99;
    }

    .label {
        width: 25%;
        border-radius: 10px 10px 0 0;
        border-bottom: solid 2px #000;
    }

}