:root {
    --ef: #efefef;
    --ff: #fff;
    --oo: #000;
}

body {
    box-sizing: border-box;
}

body {
    background-image: url(https://proprikol.ru/wp-content/uploads/2019/08/kartinki-na-zadnij-fon-18.jp);
    background-color: var(--ef);
}

.block {
    height: 35vw;
    width: 100%;
}

.content {
    background-color: var(--ff);
    height: 100%;
    font-size: calc(7px + 16 * (100vw / 1280));
}

.krug {
    height: 50px;
    margin: 3px auto;
    background: linear-gradient(to left, aqua, aquamarine, aqua);
    background-size: 200%;
    transition: 1s;
}

.krug:hover {
    background-position: right;
}

.tr {
    width: 0;
    height: 0;
    border-style: solid;
    border-width: 25px 0 25px 50px;
    border-color: transparent transparent transparent #fff;
    margin: auto;
}

.embed-container {
    position: relative;
    padding-bottom: 56.25%;
    height: 0;
    overflow: hidden;
    max-width: 100%;
}

.embed-container iframe,
.embed-container object,
.embed-container embed {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}

.trener {
    width: 300px;
}

.subcontent {
    background-color: var(--ff);
}

.radius {
    border: dodgerblue 2px solid;
    width: 100%;
    margin: 7px;
    box-shadow: 5px 3px 3px rgba(0, 255, 255, 0.224);
}

.where {
    background-color: var(--ff);
}