How to make Github diffs take advantage of screen width.

Instructions.md

Install Stylish for Chrome https://chrome.google.com/webstore/detail/stylish/fjnbnpbmkenffdnngjfgmeleoegfcffe

or Firefox https://addons.mozilla.org/en-US/firefox/addon/stylish/?src=external-userstyleshome

Create new style with the settings shown in the image below.

Overrides.css

.container {
    width: auto;
    margin-right: 25px;
    margin-left: 25px;
}

.repository-with-sidebar {
    display: -webkit-box;
    display: -moz-box;
    display: -ms-flexbox;
    display: -webkit-flex;
    display: flex;
    -webkit-box-direction: normal;
    -moz-box-direction: normal;
    -webkit-box-orient: horizontal;
    -moz-box-orient: horizontal;
    -webkit-flex-direction: row;
    -ms-flex-direction: row;
    flex-direction: row;
    -webkit-flex-wrap: nowrap;
    -ms-flex-wrap: nowrap;
    flex-wrap: nowrap;
    -webkit-box-pack: end;
    -moz-box-pack: end;
    -webkit-justify-content: flex-end;
    -ms-flex-pack: end;
    justify-content: flex-end;
    -webkit-align-content: stretch;
    -ms-flex-line-pack: stretch;
    align-content: stretch;
    -webkit-box-align: start;
    -moz-box-align: start;
    -webkit-align-items: flex-start;
    -ms-flex-align: start;
    align-items: flex-start;
    }

.repository-sidebar {
    float: none;
    -webkit-box-ordinal-group: 2;
    -moz-box-ordinal-group: 2;
    -webkit-order: 1;
    -ms-flex-order: 1;
    order: 1;
    -webkit-box-flex: 0;
    -moz-box-flex: 0;
    -webkit-flex: 0 1 38px;
    -ms-flex: 0 1 38px;
    flex: 0 1 38px;
    -webkit-align-self: stretch;
    -ms-flex-item-align: stretch;
    align-self: stretch;
    }

.repository-content {
    float: none;
    width: auto;
    margin-right: 20px;
    -webkit-box-ordinal-group: 1;
    -moz-box-ordinal-group: 1;
    -webkit-order: 0;
    -ms-flex-order: 0;
    order: 0;
    -webkit-box-flex: 1;
    -moz-box-flex: 1;
    -webkit-flex: 1 1 auto;
    -ms-flex: 1 1 auto;
    flex: 1 1 auto;
    -webkit-align-self: stretch;
    -ms-flex-item-align: stretch;
    align-self: stretch;
    }

/*
    Legacy Firefox implementation treats all flex containers
    as inline-block elements.
*/

@-moz-document url-prefix() {
.flex-container {
    width: 100%;
    -moz-box-sizing: border-box;
    }

}