The 404 and search page don’t use the background color that has been specified in the theme options. So if you set a dark background and white text, it shows white on white. This CCS forces these pages to use the correct background color.

/* -- START Fix background color on 404 and search page -- */
.error404 #main-content, .search #main-content{
background-color: initial;
}
/* -- END Fix background color on 404 and search page -- */Code language: CSS (css)

Note: you can also use the theme builder to create a template for these pages.