How to apply the same style for gridview on clicking buttons

Below is the main css that is getting applied only for the first time if i click edit the my gridview css is getting changed as shown below[my grid is getting changed in this way][1] but my actual grid should be in this way[enter image description here][2]

.mydatagrid
{
width: 100%;
border: solid 2px black;
min-width: 80%;
}


[1]: https://i.stack.imgur.com/qhINw.png
[2]: https://i.stack.imgur.com/ENMyW.png

Though i am calling my my css that is mydatagrid in my gridview but still the css is getting changed.Below is the new css and gridview code







EmptyDataText="No files uploaded" OnRowCommand="GridView1_RowCommand" OnRowDataBound="GridView1_RowDataBound" OnPageIndexChanging="GridView1_PageIndexChanging">
<%--AllowPaging="true" OnPageIndexChanging="GridView1_PageIndexChanging" PageSize="10">--%>









































Below is the main css that is getting applied only for the first time if i click edit the my gridview css ig getting changed as shown below

.mydatagrid
{
width: 100%;
border: solid 2px black;
min-width: 80%;
}



How to apply the same style for gridview on clicking buttons in gridview