I made a tweak with CSS . The file that will be modified is
wp-admin/css/colors-fresh.css
Open the file with a file-editor (I use notepad++) and find the following CSS rule .
.widget,#widget-list .widget-top,.postbox,.menu-item-settings{background-color:#f5f5f5;background-image:-ms-linear-gradient(top,#f9f9f9,#f5f5f5);background-image:-moz-linear-gradient(top,#f9f9f9,#f5f5f5);background-image:-o-linear-gradient(top,#f9f9f9,#f5f5f5);background-image:-webkit-gradient(linear,left top,left bottom,from(#f9f9f9),to(#f5f5f5));background-image:-webkit-linear-gradient(top,#f9f9f9,#f5f5f5);background-image:linear-gradient(top,#f9f9f9,#f5f5f5); XXXXX }
At the end of the rule append height: 200px .
Replace XXXXX with height: 200px ; .
The file is minified , so difficult to locate the CSS rule .Use search function of the file-editor (CTL + F ) to locate the CSS rule .
I made the test on my development environment and works ...
Back-up first the file and try it out