Test page after adding

WordPress Dashboard > Divi > Theme Options > Custom CSS and add the following:

Here is an article where you can learn about removing the sidebar: https://www.elegantthemes.com/blog/divi-resources/how-to-remove-sidebars-from-divi

As for the code, that’s the CSS. You can use any online tutorials for learning CSS.

/*** Take out the divider line between content and sidebar ***/
#main-content .container:before {background: none;}
/*** Hide Sidebar ***/
#sidebar {display:none;}
/*** Expand the content area to fullwidth ***/
@media (min-width: 981px){
#left-area {
    width: 100%;
    padding: 23px 0px 0px !important;
    float: none !important;

to Divi>theme Options>Custom Css