Thanks for your answer. I use a MacBook and open the files in the Add On "Custom Background Image and Gear Icon". Then i open css where I have several options in order to open it with text edit. This is what the code in the deckbrowser looks like:

/* night-mode-specific colours */
.review-count {
color: #0a0;
}
.new-count {
color: #00a;
}
.learn-count {
color: #C35617;
}
.zero-count {
color: #ddd;
}
.nightMode .review-count {
color: #5CcC00;
}
.nightMode .new-count {
color: #77ccff;
}
.nightMode .learn-count {
color: #FF935B;
}
.nightMode .zero-count {
color: #444;
}
/* Copyright: Ankitects Pty Ltd and contributors
* AnKingMed
* License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html */
a.deck {
color: black;
text-decoration: none;
min-width: 5em;
display: inline-block;
}
a.deck:hover {
text-decoration: underline;
}
tr.deck td {
border-bottom: 1px solid #e7e7e7;
}
tr.top-level-drag-row td {
border-bottom: 1px solid transparent;
}
td {
white-space: nowrap;
}
tr.drag-hover td {
border-bottom: 1px solid #aaa;
}
body {
margin: 1em;
-webkit-user-select: none;
}
body.nightMode {
margin: 1em;
-webkit-user-select: none;
}
.current {
background-color: rgba(231, 231, 231, 0.3)/* #e7e7e7; */
}
.decktd {
min-width: 15em;
}
.count {
min-width: 4em;
text-align: right;
}
.optscol {
width: 2em;
}
.collapse {
color: black;
text-decoration: none;
display: inline-block;
width: 1em;
}
.filtered {
color: #00a !important;
}
.gears {
width: 1em;
height: 1em;
opacity: 0.5;
padding-top: 0.2em;
}
.nightMode a.deck {
color: white;
}
.nightMode tr.deck td {
border-bottom-color: #29292B;
}
.nightMode tr.drag-hover td {
border-bottom-color: #777;
}
.nightMode .current {
background-color: rgba(41, 41, 43, 0.3); /* #29292B; */
}
.nightMode .collapse {
color: white;
}
.nightMode .gears {
filter: invert(180);
}
.nightMode .filtered {
color: #77ccff !important;
}
/*AnKing edits*/

​

Not sure wether this helps in any way.