diff --git a/phpBB/styles/prosilver/theme/cp.css b/phpBB/styles/prosilver/theme/cp.css
index 2f84fc9b12..0258104667 100644
--- a/phpBB/styles/prosilver/theme/cp.css
+++ b/phpBB/styles/prosilver/theme/cp.css
@@ -24,12 +24,12 @@
 }
 
 .panel-container .panel p {
-	font-size: 14px;
+	font-size: var(--ps-font-small);
 }
 
 .panel-container .panel ol {
-	font-size: 14px;
-	margin-left: 28px;
+	font-size: var(--ps-font-small);
+	margin-left: calc(var(--ps-font-small) * 2);
 }
 
 .panel-container .panel li.row {
@@ -80,7 +80,7 @@ ul.cplist {
 }
 
 .panel-container .postbody p.author {
-	font-size: 14px;
+	font-size: var(--ps-font-small);
 }
 
 .cp-main .buttons {
@@ -118,9 +118,9 @@ ul.cplist {
 
 .tabs .tab,
 .minitabs .tab {
-	font-size: 12px;
+	font-size: var(--ps-font-tiny);
 	font-weight: bold;
-	line-height: 18px;
+	line-height: 1.4;
 	display: block;
 	float: left;
 }
@@ -180,12 +180,12 @@ ul.cplist {
 }
 
 .responsive-tab > a.responsive-tab-link {
-	font-size: 20px;
-	line-height: 18px;
+	font-size: var(--ps-font-h3);
+	line-height: 0.875;
 	text-decoration: none;
 	position: relative;
 	display: block;
-	width: 20px;
+	width: var(--ps-font-h3);
 }
 
 .responsive-tab .responsive-tab-link:before {
@@ -201,7 +201,7 @@ ul.cplist {
 
 .tabs .dropdown,
 .minitabs .dropdown {
-	font-size: 14px;
+	font-size: var(--ps-font-small);
 	font-weight: normal;
 	top: 20px;
 	margin-right: -2px;
@@ -248,14 +248,13 @@ ul.cplist {
 
 /* Link styles for the sub-section links */
 .navigation a {
-	font-size: 12px;
+	font-size: var(--ps-font-tiny);
 	text-decoration: none;
+	border: 1px solid transparent;
+	border-radius: 4px 0 0 4px;
 	display: block;
 	margin: 1px 0;
 	padding: 5px;
-	border: 1px solid transparent;
-	border-radius: 4px 0 0 4px;
-
 }
 
 .navigation a:hover {
@@ -272,12 +271,12 @@ ul.cplist {
 
 /* Friends list */
 .cp-mini {
-	font-size: 12px;
+	font-size: var(--ps-font-tiny);
 	border-radius: 7px;
 	overflow-y: auto;
 	max-height: 200px;
-	margin: 12px 15px 12px 5px;
-	padding: 5px 12px;
+	margin: var(--ps-font-tiny) 15px var(--ps-font-tiny) 5px;
+	padding: 5px var(--ps-font-tiny);
 }
 
 dl.mini dt {
diff --git a/phpBB/styles/prosilver/theme/forms.css b/phpBB/styles/prosilver/theme/forms.css
index 288043c011..25ecb496d8 100644
--- a/phpBB/styles/prosilver/theme/forms.css
+++ b/phpBB/styles/prosilver/theme/forms.css
@@ -9,13 +9,13 @@
 ---------------------------------------- */
 fieldset {
 	font-family: Verdana, Helvetica, Arial, sans-serif;
-	font-size: 14px;
+	font-size: var(--ps-font-small);
 	border-width: 0;
 }
 
 input {
 	font-family: Verdana, Helvetica, Arial, sans-serif;
-	font-size: 14px;
+	font-size: var(--ps-font-small);
 	font-weight: normal;
 	vertical-align: middle;
 	padding: 0 3px;
@@ -23,7 +23,7 @@ input {
 
 select {
 	font-family: Verdana, Helvetica, Arial, sans-serif;
-	font-size: 14px;
+	font-size: var(--ps-font-small);
 	font-weight: normal;
 	vertical-align: middle;
 	border: 1px solid transparent;
@@ -36,18 +36,18 @@ select:focus {
 }
 
 option {
-	padding-right: 14px;
+	padding-right: var(--ps-font-small);
 }
 
 select optgroup option {
 	font-family: Verdana, Helvetica, Arial, sans-serif;
-	padding-right: 14px;
+	padding-right: var(--ps-font-small);
 }
 
 textarea {
 	font-family: "Lucida Grande", Verdana, Helvetica, Arial, sans-serif;
-	font-size: 14px;
-	line-height: 20px;
+	font-size: var(--ps-font-small);
+	line-height: 1.5;
 	width: 60%;
 	padding: 2px;
 }
@@ -184,7 +184,7 @@ fieldset.display-options a {
 }
 
 .dropdown fieldset.display-options {
-	font-size: 14px;
+	font-size: var(--ps-font-small);
 	margin: 0;
 	padding: 0;
 }
@@ -203,10 +203,10 @@ fieldset.display-options a {
 
 /* Display actions for ucp and mcp pages */
 fieldset.display-actions {
-	line-height: 28px;
+	line-height: 2;
 	text-align: right;
 	white-space: nowrap;
-	padding-right: 14px;
+	padding-right: var(--ps-font-small);
 }
 
 fieldset.display-actions label {
@@ -216,7 +216,7 @@ fieldset.display-actions label {
 
 /* Not used anywhere */
 fieldset.sort-options {
-	line-height: 28px;
+	line-height: 2;
 }
 
 /* MCP forum selection */
@@ -262,7 +262,7 @@ fieldset.submit-buttons input {
 
 .message-box textarea {
 	font-family: "Trebuchet MS", Verdana, Helvetica, Arial, sans-serif;
-	font-size: 16px;
+	font-size: var(--ps-font-normal);
 	outline: 3px dashed transparent;
 	outline-offset: -4px;
 	-webkit-box-sizing: border-box;
@@ -369,7 +369,7 @@ input.disabled {
 	float: left;
 	-webkit-box-sizing: border-box;
 	box-sizing: border-box;
-	height: 30px;
+	height: calc(var(--ps-line-height) * 1.25);
 	padding: 3px;
 }
 
diff --git a/phpBB/styles/prosilver/theme/icons.css b/phpBB/styles/prosilver/theme/icons.css
index 135f5d0675..153a755881 100644
--- a/phpBB/styles/prosilver/theme/icons.css
+++ b/phpBB/styles/prosilver/theme/icons.css
@@ -12,14 +12,14 @@ svg {
 
 .o-icon {
 	vertical-align: middle !important;
-	width: 18px;
-	height: 18px;
+	width: var(--ps-font-h4);
+	height: var(--ps-font-h4);
 }
 
 .o-icon-src-mdi,
 .o-icon-src-ic {
-	width: 22px;
-	height: 22px;
+	width: calc(var(--ps-font-h4) + 4px); /* icon + 2 * 2px padding */
+	height: calc(var(--ps-font-h4) + 4px); /* icon + 2 * 2px padding */
 }
 
 .o-icon-src-fa {
@@ -28,7 +28,7 @@ svg {
 
 .o-icon-font {
 	font-family: "Font Awesome 6 Free", "Font Awesome 6 Brands";
-	font-size: 18px;
+	font-size: var(--ps-font-h4);
 	font-style: normal;
 	font-variant: normal;
 	-webkit-font-smoothing: antialiased;
@@ -57,7 +57,7 @@ span + .o-icon {
 
 blockquote cite:before,
 .uncited:before {
-	font-size: 40px;
+	font-size: calc(var(--ps-font-normal) * 2.5);
 	vertical-align: bottom;
 	display: inline-block;
 	margin-top: 8px;
@@ -72,9 +72,9 @@ blockquote cite:before,
 
 .c-forum-row-icon,
 .c-notification-check-icon {
-	font-size: 24px;
-	width: 24px;
-	height: 24px;
+	font-size: var(--ps-font-h1);
+	width: var(--ps-font-h1);
+	height: var(--ps-font-h1);
 	margin-top: 0;
 }
 
@@ -86,8 +86,8 @@ blockquote cite:before,
 	display: inline-flex;
 	justify-content: center;
 	align-items: center;
-	width: 36px;
-	height: 36px;
+	width: calc(var(--ps-font-normal) * 2.25);
+	height: calc(var(--ps-font-normal) * 2.25);
 	margin-top: -17px;
 	margin-left: 9px;
 }
diff --git a/phpBB/styles/prosilver/theme/links.css b/phpBB/styles/prosilver/theme/links.css
index 87359530f9..2f7ac86236 100644
--- a/phpBB/styles/prosilver/theme/links.css
+++ b/phpBB/styles/prosilver/theme/links.css
@@ -69,7 +69,7 @@ a.forumtitle,
 a.topictitle,
 span.topictitle {
 	font-family: "Trebuchet MS", Helvetica, Arial, sans-serif;
-	font-size: 16px;
+	font-size: var(--ps-font-normal);
 	text-decoration: none;
 }
 
@@ -151,24 +151,24 @@ a.lastsubject:hover {
 }
 
 .top {
-	font-size: 14px;
+	font-size: var(--ps-font-small);
 	text-decoration: none;
-	margin-top: 12px;
+	margin-top: calc(var(--ps-font-small) - 2px);
 }
 
 .to-top-button {
-	position: fixed;
-	right: 24px;
-	bottom: 24px;
-	inline-size: 48px;
-	block-size: 48px;
 	border-radius: 50%;
+	position: fixed;
+	right: var(--ps-line-height);
+	bottom: var(--ps-line-height);
 	display: none;
+	block-size: calc(var(--ps-line-height) * 2);
+	inline-size: calc(var(--ps-line-height) * 2);
 }
 
 .to-top-button .o-icon {
-	font-size: 32px;
-	padding: 8px;
+	font-size: calc(var(--ps-font-normal) * 2);
+	padding: calc(var(--ps-font-normal) / 2);
 }
 
 /* Back to top of page */