.responsive-embed,
.flex-video {
    position: relative;
    height: 0;
    margin-bottom: 1rem;
    padding-bottom: 75%;
    overflow: hidden;
}

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

.responsive-embed.widescreen,
.flex-video.widescreen {
    padding-bottom: 56.25%;
}

.responsive-embed {
    position: relative;
    height: 0;
    margin-bottom: 1rem;
    padding-bottom: 75%;
    overflow: hidden;
}

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

.responsive-embed.widescreen {
    padding-bottom: 56.25%;
}

Use one class for responsive embeds
Use one class for responsive embeds
