Description

Setting fixed width of columns in IR is a little different than in older APEX version.

Here's an example of setting fixed width of Hiredate column

First you have to set column static ID:

Then you have to add CSS to page (or static file):

Update:
Use min-width instead of width CSS property (it fixes problem if you have many columns in report)

If you have more than one report on the page you can prefix CSS with region static ID, for example:
#regionStaticId th#colHiredate, #regionStaticId td[headers=colHiredate]{width:100px}
#regionStaticId th#colHiredate, #regionStaticId td[headers=colHiredate]{min-width:100px}