Replace Less with CSS (#23481)

Ran most of the Less files through the Less compiler and Prettier and
then followed up with a round of manual fixes.

The Less compiler had unfortunately stripped all `//` style comments
that I had to restore (It did preserve `/* */` comments). Other fixes
include duplicate selector removal which were revealed after the
transpilation and which weren't caught by stylelint before but now are.

Fixes: https://github.com/go-gitea/gitea/issues/15565

web_src/css/codemirror/base.css

@@ -0,0 +1,45 @@
+.ui .field:not(:last-child) .EasyMDEContainer .editor-statusbar {
+  margin-bottom: -1em; /* when there is a statusbar, the "margin-bottom: 1em" of the "field" is not needed, because the statusbar is likely a blank line */
+}
+
+.EasyMDEContainer .CodeMirror {
+  color: var(--color-input-text);
+  background-color: var(--color-input-background);
+  border-color: var(--color-secondary);
+  font: 14px var(--fonts-monospace);
+}
+
+.EasyMDEContainer .CodeMirror.cm-s-default {
+  border-radius: var(--border-radius);
+  padding: 0 !important;
+}
+
+.EasyMDEContainer .CodeMirror.CodeMirror-fullscreen.CodeMirror-focused {
+  border-right: 1px solid var(--color-primary) !important;
+}
+
+.CodeMirror-cursor {
+  border-color: var(--color-caret) !important;
+}
+
+.CodeMirror .cm-comment {
+  background: inherit !important;
+}
+
+.CodeMirror .CodeMirror-code {
+  font: 14px var(--fonts-monospace);
+}
+
+.CodeMirror-selected {
+  background: var(--color-primary-light-1) !important;
+  color: var(--color-white) !important;
+}
+
+.CodeMirror-placeholder {
+  color: var(--color-placeholder-text) !important;
+  opacity: 1 !important;
+}
+
+.CodeMirror-focused {
+  border-color: var(--color-primary) !important;
+}

web_src/css/codemirror/dark.css

@@ -0,0 +1,106 @@
+.CodeMirror.cm-s-default .cm-property,
+.CodeMirror.cm-s-paper .cm-property {
+  color: #a0cc75;
+}
+
+.CodeMirror.cm-s-default .cm-header,
+.CodeMirror.cm-s-paper .cm-header {
+  color: #9daccc;
+}
+
+.CodeMirror.cm-s-default .cm-quote,
+.CodeMirror.cm-s-paper .cm-quote {
+  color: #009900;
+}
+
+.CodeMirror.cm-s-default .cm-keyword,
+.CodeMirror.cm-s-paper .cm-keyword {
+  color: #cc8a61;
+}
+
+.CodeMirror.cm-s-default .cm-atom,
+.CodeMirror.cm-s-paper .cm-atom {
+  color: #ef5e77;
+}
+
+.CodeMirror.cm-s-default .cm-number,
+.CodeMirror.cm-s-paper .cm-number {
+  color: #ff5656;
+}
+
+.CodeMirror.cm-s-default .cm-def,
+.CodeMirror.cm-s-paper .cm-def {
+  color: #e4e4e4;
+}
+
+.CodeMirror.cm-s-default .cm-variable-2,
+.CodeMirror.cm-s-paper .cm-variable-2 {
+  color: #00bdbf;
+}
+
+.CodeMirror.cm-s-default .cm-variable-3,
+.CodeMirror.cm-s-paper .cm-variable-3 {
+  color: #008855;
+}
+
+.CodeMirror.cm-s-default .cm-comment,
+.CodeMirror.cm-s-paper .cm-comment {
+  color: #8e9ab3;
+}
+
+.CodeMirror.cm-s-default .cm-string,
+.CodeMirror.cm-s-paper .cm-string {
+  color: #a77272;
+}
+
+.CodeMirror.cm-s-default .cm-string-2,
+.CodeMirror.cm-s-paper .cm-string-2 {
+  color: #ff5500;
+}
+
+.CodeMirror.cm-s-default .cm-meta,
+.CodeMirror.cm-s-paper .cm-meta,
+.CodeMirror.cm-s-default .cm-qualifier,
+.CodeMirror.cm-s-paper .cm-qualifier {
+  color: #ffb176;
+}
+
+.CodeMirror.cm-s-default .cm-builtin,
+.CodeMirror.cm-s-paper .cm-builtin {
+  color: #b7c951;
+}
+
+.CodeMirror.cm-s-default .cm-bracket,
+.CodeMirror.cm-s-paper .cm-bracket {
+  color: #999977;
+}
+
+.CodeMirror.cm-s-default .cm-tag,
+.CodeMirror.cm-s-paper .cm-tag {
+  color: #f1d273;
+}
+
+.CodeMirror.cm-s-default .cm-attribute,
+.CodeMirror.cm-s-paper .cm-attribute {
+  color: #bfcc70;
+}
+
+.CodeMirror.cm-s-default .cm-hr,
+.CodeMirror.cm-s-paper .cm-hr {
+  color: #999999;
+}
+
+.CodeMirror.cm-s-default .cm-url,
+.CodeMirror.cm-s-paper .cm-url {
+  color: #c5cfd0;
+}
+
+.CodeMirror.cm-s-default .cm-link,
+.CodeMirror.cm-s-paper .cm-link {
+  color: #d8c792;
+}
+
+.CodeMirror.cm-s-default .cm-error,
+.CodeMirror.cm-s-paper .cm-error {
+  color: #dbdbeb;
+}

web_src/css/codemirror/light.css

@@ -0,0 +1 @@
+/* Placeholder, there is no light theme, it uses CM defaults */