stylesheet.css

:root {
    --nr-videos-per-row: 6; /* number of videos per row */
    --grid-padding: 5vw; /* left and right padding of main grid */
    --display-avatar: none; /* to enable: inline-block */
}

ytd-rich-grid-renderer {
    --ytd-rich-grid-items-per-row: var(--nr-videos-per-row)!important;
}

ytd-rich-grid-row {
    width: unset;
}

ytd-rich-grid-row > #contents.ytd-rich-grid-row {
    flex-direction: column;
    margin: 0;
}

ytd-rich-grid-row > #contents > ytd-rich-item-renderer {
    margin-right: 4px;
    margin-left: 0;
    display: inline-block;
    width: calc((80vw - 2 * var(--grid-padding)) / var(--nr-videos-per-row));
    height: calc((80vw - 2 * var(--grid-padding)) / var(--nr-videos-per-row));
    margin-bottom: 24px;
}


ytd-rich-grid-renderer > div#contents.style-scope.ytd-rich-grid-renderer {
    padding: 0 var(--grid-padding);
    max-width: calc(100% - 2 * var(--grid-padding));
    display: flex;
    justify-content: start;
}

a#video-title.yt-simple-endpoint.style-scope.ytd-rich-grid-video-renderer {
    font-size: 1.4rem;
}

div#metadata * {
    font-size: 1.3rem!important;
}

a#avatar-link {
    display: var(--display-avatar);
}

@media screen and (max-width: 768px) {
    :root {
        --nr-videos-per-row: 2;
    }
}

@media screen and (min-width: 769px) and (max-width: 1024px) {
    :root {
        --nr-videos-per-row: 3;
    }
}

@media screen and (min-width: 1025px) and (max-width: 1200px) {
    :root {
        --nr-videos-per-row: 4;
    }
}

@media screen and (min-width: 1201px) and (max-width: 1600px) {
    :root {
        --nr-videos-per-row: 5;
    }
}