Column font and width not changing, rest of the table is

Question

I have a document library with scripts to change the font size of the header row. All the columns apart from one; "Short Description"; have changed.

I have just added a script to adjust the column width of this column and it's not responding to that either.

I have tested the script on other columns in the table and it works fine.

Its a Multiple Line Text column. The colour changes for the header row and font have both worked.

Any ideas?

Scripts being used are:

    <script 
src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js" 
type="text/javascript">
</script>
<script type="text/javascript">
$(function(){
$("div.ms-vh-div:contains('Topic')").css("width", "500px");});
</script>

and

    <style>
.ms-viewheadertr a,
.ms-viewheadertr div {
color: white;
}
.ms-vh2 {
font-size: 10pt ! important; }
.ms-vh {
font-size: 10pt ! important; }
.ms-viewheadertr {
font-size: 10pt ! important; }
.ms-viewheadertr {
background-color: #00646e; }
</style>

Answer 1

Problem Solved. I have faced these situation multiple times and solved by using simple styling. Here I have picked up the header element by its position. Here the column MLOT (multiple Line of Text) is at 7th position. You can choose based on your field's sequence. I have used Script editor web part for this. pls Refer below script:

<style type="text/css">
.ms-listviewtable thead tr th:nth-child(7){
    color: red !important;
    width: 250px !important;
    font-size: xx-large !important;
}
</style> 

Screen Shot:

Answer 2

Put a script editor web part on the page and add following code. This will change the header styling.

<style>
.ms-listviewtable th{font-size: 24px;}
</style>

If you want to change the header of only one column then use script suggested by @DvG