This should fix most of the HoundCI errors. Still a few remaining but I'll leave that to @ciar4n to take care of it. Here is the list:

dimitris@Mars  ~/Documents/github_projects/joomla1/administrator/templates/atum/scss   patch-7 ●✚  scss-lint
blocks/_alerts.scss:35:1 [W] SelectorFormat: Selector fullWidth should be written in lowercase with hyphens
blocks/_alerts.scss:62:1 [W] SelectorFormat: Selector fullWidth should be written in lowercase with hyphens
blocks/_header.scss:87:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
blocks/_icons.scss:30:1 [W] QualifyingElement: Avoid qualifying attribute selectors with an element.
blocks/_icons.scss:30:1 [W] QualifyingElement: Avoid qualifying attribute selectors with an element.
blocks/_icons.scss:32:13 [W] ColorVariable: Color literals like #ccc should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_icons.scss:34:12 [W] ColorVariable: Color literals like #ccc should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_login.scss:73:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_login.scss:73:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
blocks/_login.scss:74:16 [W] ColorVariable: Color literals like #c6d2de should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_modals.scss:11:12 [W] ColorVariable: Color literals like #fff should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_modals.scss:14:14 [W] ColorVariable: Color literals like #fff should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_searchtools.scss:13:30 [W] ColorVariable: Color literals like rgba(0, 0, 0, 0.05) should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_searchtools.scss:35:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_searchtools.scss:35:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
blocks/_searchtools.scss:46:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
blocks/_searchtools.scss:47:21 [W] ColorVariable: Color literals like #fefefe should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_searchtools.scss:49:16 [W] ColorVariable: Color literals like #fff should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_searchtools.scss:52:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_searchtools.scss:52:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
blocks/_searchtools.scss:53:27 [W] ColorVariable: Color literals like #fff should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_sidebar.scss:46:33 [W] ColorVariable: Color literals like rgba(0, 0, 0, 0.5) should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_sidebar.scss:50:25 [W] ColorVariable: Color literals like #fff should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_sidebar.scss:52:33 [W] ColorVariable: Color literals like rgba(0, 0, 0, 0.3) should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_sidebar.scss:92:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
blocks/_sidebar.scss:98:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
blocks/_sidebar.scss:100:21 [W] ColorVariable: Color literals like #78aeda should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_sidebar.scss:101:9 [W] PropertySortOrder: Properties should be ordered box-shadow, outline, text-decoration
blocks/_sidebar.scss:138:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_sidebar.scss:138:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
blocks/_sidebar.scss:143:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_sidebar.scss:143:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
blocks/_sidebar.scss:170:1 [W] MergeableSelector: Merge rule li li with rule on line 80
blocks/_sidebar.scss:175:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_sidebar.scss:179:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_sidebar.scss:179:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
blocks/_sidebar.scss:185:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_sidebar.scss:189:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_sidebar.scss:228:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_sidebar.scss:228:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
blocks/_sidebar.scss:229:9 [W] ImportantRule: !important should not be used
blocks/_sidebar.scss:237:5 [W] SpaceAfterPropertyColon: Colon after property should be followed by one space
blocks/_sidebar.scss:240:5 [W] ImportantRule: !important should not be used
blocks/_sidebar.scss:245:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_sidebar.scss:258:1 [W] QualifyingElement: Avoid qualifying class selectors with an element.
blocks/_sidebar.scss:279:5 [W] PropertySortOrder: Properties should be ordered overflow, width
blocks/_sidebar.scss:284:5 [W] ImportantRule: !important should not be used
blocks/_sidebar.scss:301:3 [W] ImportantRule: !important should not be used
blocks/_sidebar.scss:302:3 [W] ImportantRule: !important should not be used
blocks/_status.scss:4:3 [W] PropertySortOrder: Properties should be ordered background, border-top, box-shadow, color, margin-left, padding, transition, transition-delay, z-index
blocks/_status.scss:7:10 [W] ColorVariable: Color literals like #626262 should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_status.scss:8:15 [W] ColorVariable: Color literals like #ebebeb should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_status.scss:9:15 [W] ColorVariable: Color literals like #d4d4d4 should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_status.scss:10:34 [W] SpaceAfterComma: Commas in function arguments should be followed by one space
blocks/_status.scss:20:5 [W] PropertySortOrder: Properties should be ordered color, font-size
blocks/_status.scss:21:12 [W] ColorVariable: Color literals like #555 should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_toolbar.scss:4:3 [W] PropertySortOrder: Properties should be ordered background, color, left, min-height, padding, position, right, top, width, z-index
blocks/_toolbar.scss:12:10 [W] ColorVariable: Color literals like #0c192e should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_toolbar.scss:16:5 [W] PropertySortOrder: Properties should be ordered margin-left, margin-right
blocks/_toolbar.scss:24:7 [W] PropertySortOrder: Properties should be ordered box-shadow, margin-left
blocks/_toolbar.scss:27:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
blocks/_toolbar.scss:34:5 [W] PropertySortOrder: Properties should be ordered color, font-size, line-height, padding
blocks/_toolbar.scss:37:12 [W] ColorVariable: Color literals like white should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_toolbar.scss:37:12 [W] ColorKeyword: Color white should be written in hexadecimal form as #ffffff
blocks/_toolbar.scss:43:7 [W] PropertySortOrder: Properties should be ordered background-color, color, display, height, line-height, margin, width, z-index
blocks/_toolbar.scss:49:14 [W] ColorVariable: Color literals like white should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_toolbar.scss:49:14 [W] ColorKeyword: Color white should be written in hexadecimal form as #ffffff
blocks/_toolbar.scss:50:25 [W] ColorVariable: Color literals like rgba(0, 0, 0, 0.2) should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_toolbar.scss:61:7 [W] PropertySortOrder: Properties should be ordered background-color, margin-right
blocks/_toolbar.scss:71:25 [W] ColorVariable: Color literals like rgba(0, 0, 0, 0.2) should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_treeselect.scss:18:25 [W] ColorVariable: Color literals like rgba(0, 0, 0, 0.2) should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_treeselect.scss:29:25 [W] ColorVariable: Color literals like rgba(0, 0, 0, 0.2) should only be used in variable declarations; they should be referred to via variable everywhere else.
blocks/_treeselect.scss:41:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
blocks/_treeselect.scss:51:1 [W] TrailingWhitespace: Line contains trailing whitespace
blocks/_treeselect.scss:61:5 [W] PropertySortOrder: Properties should be ordered cursor, display, margin-right, padding, text-align
blocks/_treeselect.scss:106:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_treeselect.scss:112:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_treeselect.scss:116:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
blocks/_treeselect.scss:119:1 [W] EmptyLineBetweenBlocks: Rule declaration should be followed by an empty line
pages/_com_config.scss:3:1 [W] SelectorFormat: Selector com_config should be written in lowercase with hyphens
pages/_com_cpanel.scss:3:1 [W] SelectorFormat: Selector com_cpanel should be written in lowercase with hyphens
pages/_com_cpanel.scss:22:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
pages/_com_cpanel.scss:22:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
pages/_com_cpanel.scss:27:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
pages/_com_cpanel.scss:27:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
pages/_com_cpanel.scss:47:7 [W] PropertySortOrder: Properties should be ordered color, display, height, line-height, text-align, width
pages/_com_modules.scss:3:1 [W] SelectorFormat: Selector com_modules should be written in lowercase with hyphens
pages/_com_templates.scss:15:7 [W] PropertySortOrder: Properties should be ordered backface-visibility, column-break-inside, display, list-style, margin-bottom, vertical-align, width
pages/_com_templates.scss:25:23 [W] ColorVariable: Color literals like #fafafa should only be used in variable declarations; they should be referred to via variable everywhere else.
pages/_com_templates.scss:26:13 [W] ColorVariable: Color literals like #ddd should only be used in variable declarations; they should be referred to via variable everywhere else.
pages/_com_users.scss:3:1 [W] SelectorFormat: Selector com_users should be written in lowercase with hyphens
pages/_com_users.scss:5:1 [W] TrailingWhitespace: Line contains trailing whitespace
template-rtl.scss:18:5 [W] PropertySortOrder: Properties should be ordered left, right
template-rtl.scss:36:5 [W] PropertySortOrder: Properties should be ordered left, right
template-rtl.scss:102:41 [W] SpaceAfterComma: Commas in function arguments should be followed by one space
template-rtl.scss:164:5 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
template-rtl.scss:182:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
template-rtl.scss:199:1 [W] SelectorFormat: Selector com_cpanel should be written in lowercase with hyphens
template-rtl.scss:205:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
template-rtl.scss:205:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
template-rtl.scss:210:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
template-rtl.scss:210:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
template-rtl.scss:220:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
template-rtl.scss:220:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
template-rtl.scss:222:23 [W] ColorVariable: Color literals like #ccc should only be used in variable declarations; they should be referred to via variable everywhere else.
template.scss:62:3 [W] PropertySortOrder: Properties should be ordered background-color, min-height, position
template.scss:76:3 [W] PropertySortOrder: Properties should be ordered border-radius, padding-top
template.scss:80:5 [W] PropertySortOrder: Properties should be ordered margin-left, margin-right
template.scss:83:1 [W] TrailingWhitespace: Line contains trailing whitespace
template.scss:95:3 [W] ImportantRule: !important should not be used
template.scss:103:1 [W] MergeableSelector: Merge rule .item-associations li with rule on line 99
vendor/_chosen.scss:41:1 [W] SelectorDepth: Selector should have depth of applicability no greater than 3, but was 4
vendor/_chosen.scss:59:3 [W] ImportantRule: !important should not be used
vendor/_chosen.scss:64:3 [W] ImportantRule: !important should not be used
vendor/_chosen.scss:67:5 [W] ImportantRule: !important should not be used
vendor/_dragula.scss:5:27 [W] ColorVariable: Color literals like #90ee90 should only be used in variable declarations; they should be referred to via variable everywhere else.
vendor/_dragula.scss:7:3 [W] ImportantRule: !important should not be used
vendor/_dragula.scss:9:3 [W] ImportantRule: !important should not be used
vendor/_dragula.scss:10:3 [W] ImportantRule: !important should not be used
vendor/bootstrap/_custom-forms.scss:11:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
vendor/bootstrap/_custom-forms.scss:22:7 [W] NestingDepth: Nesting should be no greater than 3, but was 4
vendor/bootstrap/_dropdown.scss:33:25 [W] ColorVariable: Color literals like rgba(0, 0, 0, 0.1) should only be used in variable declarations; they should be referred to via variable everywhere else.
vendor/bootstrap/_nav.scss:23:26 [W] ColorVariable: Color literals like rgba(0, 0, 0, 0.1) should only be used in variable declarations; they should be referred to via variable everywhere else.

✘ dimitris@Mars  ~/Documents/github_projects/joomla1/administrator/templates/atum/scss   patch-7 ●✚ 