Hello @Nohbdy
you doing great well done and here are my notice

there issue in the preview area so i will ask @schalkneethling to help to fix this

for the gap part the point :
a) the rule take part of the gap so if there there 20 gap and 5px for rule as you did it would look like if there 7.5px on right side of column then 5px for rule then another 7.5px for the left side of the next rule
they already mentioned it in the lesson but it hard to get it without use it
Something to take note of is that the rule doesn't take up any width of its own. It lies across the gap you created with
columngap. To make more space on either side of the rule, you'll need to increase the
columngap size.
so the gap to be calculated it will be the double of the required space (one for the right side of column and another for left side of the next column) + the rule size if there is any
so the answer would be
.container {
columnwidth: 200px;
columnrule: 5px solid gray;
columngap: 25px;
}
hope that help and have a nice day