fix(guide): simplify directory structure

guide/english/certifications/responsive-web-design/css-grid/add-columns-with-grid-template-columns/index.md

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+---
+title: Add Columns with grid-template-columns
+---
+## Add Columns with grid-template-columns
+
+In this challenge, you are required to define columns for the grid.
+
+### Hint
+
+You can define columns by declaring the following in your CSS codeblock:
+
+````css
+grid-template-columns: parameters;
+````
+
+where parameters is whatever you want it to be.
+
+### Solution
+
+Since the challenge requires you to create three columns of 100px each, declare the followin in your .container CSS codeblock:
+
+````css
+grid-template-columns: 100px 100px 100px;
+````