Tab Search: Minor CSS tweaks to align appearance to mocks

Updated CSS to better align with figma mocks. Aligned hover
color values to those used in the new-tab-page.

before:
  https://drive.google.com/file/d/14924TmDxdzhC6CepFJSn6BxT-hWc3OXc
after:
  https://drive.google.com/file/d/1S7j2xX_nlUXOuSQkN8Sl0kaq67mrdel9

Bug: 1099917
Change-Id: Ia369ea168740309c2dff12ad384ed8c0090d584d
Reviewed-on: https://chrome-internal-review.googlesource.com/c/chrome/browser/resources/tab_search/+/3197970Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819575}

chrome/browser/resources/tab_search_merge/tab_search_item.html

 <style>
   /* TODO(crbug.com/1110109): Add dark mode support. */
   :host {
-    --horizontal-margin: 16px;
+    --horizontal-margin: 8px;
     --vertical-margin: 12px;
     align-items: center;
     background-color:  white;
@@ -10,7 +10,7 @@
   }
 
   :host-context(.selected, :host:hover) {
-    background-color: var(--cr-focused-item-color);
+    background-color: rgba(var(--google-grey-900-rgb), 0.1);
   }
 
   :host-context(.selected, :host:hover) .button-container {
@@ -36,6 +36,7 @@
   .secondary-text {
     overflow: hidden;
     text-overflow: ellipsis;
+    user-select: none;
     white-space: nowrap;
   }
 

chrome/browser/resources/tab_search_merge/tab_search_page.html

@@ -7,7 +7,6 @@
   <style>
     html,
     body {
-      height: 100%;
       width: 320px;
     }
 

chrome/browser/resources/tab_search_merge/tab_search_search_field.html

@@ -5,6 +5,7 @@
     border-radius: 32px;
     display: flex;
     height: 28px;
+    margin: 8px;
     padding: 0 8px;
     user-select: none;
   }