Various CSS tweaks (#21244)

- Remove arc-green specific rules and instead fix the colors in the base
rules.
- Make file table row border visible on arc-green.
- Remove remnants of fomantic accordeon module that was removed.

web_src/less/themes/theme-arc-green.less

@@ -94,7 +94,7 @@
   /* target-based colors */
   --color-body: #383c4a;
   --color-box-header: #404652;
-  --color-box-body: #303440;
+  --color-box-body: #2a2e3a;
   --color-box-body-highlight: #353945;
   --color-text-dark: #dbe0ea;
   --color-text: #bbc0ca;
@@ -105,7 +105,7 @@
   --color-footer: #2e323e;
   --color-timeline: #4c525e;
   --color-input-text: #d5dbe6;
-  --color-input-background: #292d39;
+  --color-input-background: #232933;
   --color-input-border: #454a57;
   --color-input-border-hover: #505667;
   --color-navbar: #2a2e3a;
@@ -132,25 +132,13 @@
   --color-caret: var(--color-text); /* should ideally be --color-text-dark, see #15651 */
   --color-reaction-bg: #ffffff12;
   --color-reaction-active-bg: var(--color-primary-alpha-40);
+  --color-header-bar: #2e323e;
 }
 
 ::-webkit-calendar-picker-indicator {
   filter: invert(.8);
 }
 
-.ui.horizontal.segments > .segment {
-  background-color: #383c4a;
-}
-
-.following.bar.light {
-  background: #2e323e;
-  border-color: var(--color-secondary-alpha-40);
-}
-
-.following.bar .top.menu a.item:hover {
-  color: #fff;
-}
-
 .ui.red.label,
 .ui.red.labels .label {
   background-color: #7d3434 !important;
@@ -163,10 +151,6 @@
   background-color: #936e00 !important;
 }
 
-.ui.accordion .title:not(.ui) {
-  color: #dbdbdb;
-}
-
 .ui.green.label,
 .ui.green.labels .label,
 .ui.basic.green.label {
@@ -183,19 +167,6 @@ a.ui.basic.green.label:hover {
   color: #fff !important;
 }
 
-.ui.divider:not(.vertical,.horizontal) {
-  border-bottom-color: var(--color-secondary);
-  border-top-color: transparent;
-}
-
-.form .help {
-  color: #7f8699;
-}
-
-.ui .text.light.grey {
-  color: #7f8699 !important;
-}
-
 .ui.form .fields.error .field textarea,
 .ui.form .fields.error .field select,
 .ui.form .fields.error .field input:not([type]),
@@ -257,45 +228,6 @@ a.ui.basic.green.label:hover {
   background-color: #a0cc75;
 }
 
-.ui.search > .results {
-  background: #383c4a;
-  border-color: var(--color-secondary);
-}
-
-.ui.search > .results .result:hover,
-.ui.category.search > .results .category .result:hover {
-  background: var(--color-secondary);
-}
-
-.ui.search > .results .result .title {
-  color: #dbdbdb;
-}
-
-.ui.table > thead > tr > th {
-  background: var(--color-secondary);
-  color: #dbdbdb !important;
-}
-
-.repository.file.list #repo-files-table tr {
-  background: #2a2e3a;
-}
-
-.repository.file.list #repo-files-table tr:hover {
-  background-color: #393d4a !important;
-}
-
-.overflow.menu .items .item {
-  color: #9d9d9d;
-}
-
-.overflow.menu .items .item:hover {
-  color: #dbdbdb;
-}
-
-.ui.list > .item > .content {
-  color: var(--color-secondary-dark-6) !important;
-}
-
 .repository .navbar .active.item,
 .repository .navbar .active.item:hover {
   border-color: transparent !important;
@@ -305,20 +237,6 @@ a.ui.basic.green.label:hover {
   border-color: var(--color-secondary);
 }
 
-.tag-code,
-.tag-code td {
-  background: #353945 !important;
-
-}
-.tag-code td.lines-num {
-  background-color: #3a3e4c !important;
-}
-
-.tag-code td.lines-type-marker,
-td.blob-hunk {
-  color: #dbdbdb !important;
-}
-
 .ui.red.button,
 .ui.red.buttons .button {
   background-color: #7d3434;
@@ -344,10 +262,6 @@ td.blob-hunk {
   border-color: var(--color-secondary) !important;
 }
 
-td.blob-excerpt {
-  background-color: rgba(0, 0, 0, .15);
-}
-
 .lines-code.active,
 .lines-code .active {
   background: #534d1b !important;