How to make adaptive 3 columns?

I did 6 columns, that's not as not fails to make 3 columns below only showed 6 on the website product on 3 columns, how to implement it? At the moment I have 6 columns by 12 products, I need 3 columns on 6 products

Only without bootstrap

here's the code:
July 12th 19 at 17:03
1 answer
July 12th 19 at 17:05
Like a lot of code)

.container ul li{
 list-style: none;
 float: left;
 font: 10px/1.5 Verdana, Helvetica; Sans-serif;
 width: 32%;
 margin-right: 2%;
 margin-bottom: 40px;
.container ul li:nth-child(3n){
 margin-right: 0;

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