chore: Add bootstrap variable_overrides
This MR migrates a subset of the variable overrides definition in gitlab-ce. I left out the following variables overrides:
$btn-line-height: 20px;
$input-disabled-bg: $gray-700;
$input-border-color: $gray-200;
$input-color: $gray-900;
$input-font-size: $gl-type-scale-base;
$zindex-modal-backdrop: 1040;
$nav-divider-margin-y: ($grid-size / 2);
$dropdown-divider-bg: $gray-200;
$dropdown-item-padding-y: 8px;
$dropdown-item-padding-x: 12px;
$popover-max-width: 300px;
$popover-border-width: 1px;
$popover-border-color: $border-color;
$popover-box-shadow: 0 $border-radius-small $border-radius-default 0 $shadow-color;
$popover-arrow-outer-color: $shadow-color;
I left them out based on the criteria that these variables override component styles that we’ll eventually implement in gitlab-ui.