how to change the width of the left column in Admin

The width of the Admin left column is controlled by the css below.

If the css width is removed, the column width will default to 200px as specified in admin/include/left-column.php.

File: admin/includes/stylesheet.css, line 262

.menu-container {
  background-color: #f8f8f8;
  width: ???px;  // default is 180px
  border-right: solid 2px #ccc;
  padding-top: 12px;
  padding-bottom: 12px;
}

Change the ???px value to the desired width in pixels.