I have a custom webpart called `Available` seminars: [![webpart][1]][1] I want to modify the width of certain columns. On the Internet it is written that I have to use <style type='text/css'> .ms-vh-div[DisplayName='<ColumnName>'] { width: 250px; } </style> But the problem is that I can't edit the source of Available Seminars. (See the blue border in the image). I can edit the source of my content editor, but not of my custom webpart. When I click on Edit Source, this shows up: <div class="ms-rtestate-read ms-rte-wpbox" contenteditable="false" unselectable="on"> <div class="ms-rtestate-notify ms-rtestate-read 75788cb9-fede-4c30-931f-34dfb6a75048" id="div_75788cb9-fede-4c30-931f-34dfb6a75048" unselectable="on"> </div> <div id="vid_75788cb9-fede-4c30-931f-34dfb6a75048" unselectable="on" style="display: none;"> </div> </div> <div class="ms-rtestate-read ms-rte-wpbox" contenteditable="false" unselectable="on"> <div class="ms-rtestate-notify ms-rtestate-read 1ba441c2-b2e9-42a7-b0cc-506e02119f5c" id="div_1ba441c2-b2e9-42a7-b0cc-506e02119f5c" unselectable="on"> </div> <div id="vid_1ba441c2-b2e9-42a7-b0cc-506e02119f5c" unselectable="on" style="display: none;"> </div> </div> <div class="ms-rtestate-read ms-rte-wpbox" contenteditable="false" unselectable="on"> <div class="ms-rtestate-notify ms-rtestate-read 92217f41-4296-4700-9b00-0a556b46141d" id="div_92217f41-4296-4700-9b00-0a556b46141d" unselectable="on"> </div> <div id="vid_92217f41-4296-4700-9b00-0a556b46141d" unselectable="on" style="display: none;"> </div> </div> <br/> And when I add <style type='text/css'> .ms-vh-div[DisplayName='<Title>'] { width: 450px; } </style> then nothing happens. Does someone know a solution to this? Here's what shows up when I go to title with the dev tools: [![enter image description here][2]][2] [1]: https://i.sstatic.net/ntFIU.png [2]: https://i.sstatic.net/AooGo.png