Targeting Spacing Between Columns

Hello,

I would like to target the spacing between columns in a specific row. I applied the custom CSS class ‘video-section’ and then targeted that in the General Settings Custom CSS section, but the custom CSS doesn’t seem to apply. Can you help me understand what I’m doing wrong?

Here’s what the code looks like now:

div .av_one_third {
    margin-left: 6%;
    width: 29.333333333333332%;
}

Here’s what how I’ve targeted it:

.video-section #div .av_one_third {
    margin-left: 4%;
    width: 30.633333333333332%;
}

Here’s what it looks like now: https://imgur.com/a/OBuIK0M

Here’s what I want it to look like: https://imgur.com/a/Jz1mVyb

Thank you!