Login to your SharePoint list/library.
Click Gear icon on top right hand side and click Edit page.
Click Add a Web Part link.
Select Content Editor Web part under the category Media and Content. Click Add.
Click “Click here to add new content”.
Click Edit Source.
Add CSS given below and click OK.
<style type='text/css'>
.ms-vh-div[DisplayName='<ColumnName>'] {
width: 250px;
}
</style>
Click Stop Editing.
Now, we can see the increase in the width.?
Conclusion
In this article, I explained how to increase the SharePoint list column width, using CSS.